THE

Glasgow Medical Journal.

No. I. July, 1926.

ORIGINAL ARTICLES.

WATER: ITS PHYSIOLOGICAL SIGNIFICANCE.'

By E. P. CATHCART, C.B.E., M.D., F.R.S., Professor of Chemical Physiology, University of Glasgow.

"Ohne Wasser kein Leben," as Tangl puts it, is literally true, for it can be clearly demonstrated that water is absolutely essential if life, in all forms of living matter, is to continue. Withdrawal of water, indeed, brings about the death of man much more rapidly and more painfully than the absence of food. A mammal may survive thirty, forty, fifty days or even longer, losing almost all the fat in its body and 50 per cent of its protein, if deprived of food, but if water be withheld, death takes place when it has lost little more than 10 per cent of its water content. There is then some reason for the statement of Rubner that the regulation of the water content " of the tissues is, so to speak, anxiously supervised by Nature." Nor is it wonderful that this anxious supervision is necessary when it is remembered what a very large proportion of the * A lecture delivered before the Biological Section of the Royal Philosophical Society of Glasgow, on 12th March, 1926. No. x. Vol. cvi. 2 Prof. E. P. Cathcart? Water:

body weight, even of the higher mammals, is due to water. Thus, it has been shown that the average water content of invertebrates ranges from 78 to 88 per cent, although in the case of some (e.g., Rhizostoma Cuvieri) it may be over 95 per cent. In the case of man the average ranges from 58 to 65 per cent, the variation being for the most part dependent on the fat content of the subject. Thus, with 19 per cent fat there was 60 per cent water, and when the fat content was 13 per cent the water rose to 66 per cent. This variation in water content is clearly seen in the data, calculated from the figures of Lawes and Gilbert by Wolff, for animals:?

ox. SHEEP. PIG.

Per cent. Per cent. Per cent. Fat, 191 301 18-7 35 6 23*3 42*2

Water calculated on Water, 51*5 45 5 57 3 43*4 551 4i .3 / \total live weights.

^ater calcu^ate(J on 70-9 71 *2 76-5 74*3 77 0 76 *8 / \ fat-free tissues. That the variation in water content is conditioned by the fat content is very clearly demonstrated by reference to the of the water uniformity content calculated on fat-free tissue. But, as workers have many shown, the age of the organism an plays important role. As Tangl points out, the alteration of the water content of organised tissue substance during would seem to ontogeny express an alteration which the animal organism also in the course undergoes of phylogeny. He thus correlates the alteration in water content due to age with the observations that the phylogenetically lower standing inver- tebrates, even those which do not live in water, are richer in water than the higher standing vertebrates. The following figures show that and clearly before, at, birth the tissues are much richer in water than they are later:? HENS. CATS. HUMAN. Embryo in egg. Water per cent. Water per cent. Water per cent. 7th . . . 92*8 day, . Newborn, 80-8 3rd foetal 14th . 94-0 . . 87 *3 month, day, 9 days old, . 79*7 . 21st . . New-born, 66-68 day, . 80'4 14 days old, 73*8 . Just before A(*ult, . 53.05 hatching, 78*7 83 day8 old, 66*7 is n not possible that the lowered metabolism of old be due in age may large part to a steadily increasing dessication ? Its Physiological Significance. 3

But, naturally, the water is not uniformly distributed throughout the body, nor is it by any means chiefly found in the blood and lymph. Thus, in the human body most elaborate estimations have been made, and the following table gives a very good idea of the average distribution:?

PERCENTAGE DISTRIBUTION OF WATER (VOLKMANN).

Muscle, . 50*8 Intestine, . 3*2 Fat tissue, . 2*3 Skeleton, . 12*5 Liver,. .2*8 Kidneys, . .0*6 Skin, . .6*6 Brain,. . 2*7 Spleen, . . 0*4 Blood, . 4*7 Lungs, . 2*4 Rest of body, . 11*0

The muscles, then, are seen to be the great storehouse of water in the body. In the analyses given above the actual amount of water obtained from the muscle amounted to over 20 kilo- grammes, or about one-third of the body weight. It is very manifest that the water of the circulating fluids forms but a small part of the water present in the body. The main part of the water is found, not, it is true, in the free state, but as imbibition water, in the protoplasm of the cell. This, of course, lends point to the statement of Starling that all the chemical changes which are considered under the term metabolism relate to changes in and between substances in solution. This contention may be rendered more general if it be remembered, as Haldane has pointed out, that all biological phenomena can be resolved into metabolic phenomena. One may therefore say that the whole of the processes which make up the life of the living organism, be it animal or vegetable, are ultimately referable to changes which take place in solution. What, then, are the nature and properties of this all-important constituent ? Both in its physical and its chemical properties water holds a unique position even in the physical world. If the physical characters of this familiar, unique, and wonderful fluid be tirst considered owing to its very high specific heat, or heat capacity, it not only plays an all-important rdle in regulating the temperature of the environment, but also within the organism this high specific heat allows of large changes in heat formation with but small alterations of body temperature. If, for instance, the body had a specific heat like the ordinary range of materials it would mean that temperature regulation would become exceedingly difficult, if not impossible. Further, this 4 Prof. E. P. Cathcart? Water:

constancy of body temperature plays an important part in the control of the rate of the various chemical reactions which go on in the tissues where a relatively slight rise in temperature might bring about an untoward result, such as the coagulation of protein. The latent heat of evaporation, on the one hand, of water is the highest known, and it plays a very important rdle in the control of body temperature. No other fluid can fix so much heat during evaporation, hence it follows that the loss of a comparatively small amount of fluid in the form of sweat leads to a relatively large loss of heat. On the other hand, the high latent heat of melting is a protection against freezing of the tissues. The thermal conductivity, too, of water is a maximum the among ordinary fluids, and this, of course, plays its part in heat regulation, more particularly in the rapid of heat in the equalisation body, thus doing away with the risk of such as disturbance, overheating at any one point in active muscle. On the chemical side, too, water possesses many unique As a solvent no can properties. fluid compare with water, for, in addition to the fact that water can hold in solution a most wonderful variety of substances, these substances undergo but little chemical One has change. only to consider for a moment the of variety substances which are found in solution in the blood or the plasma, still more wonderful and heterogeneous collection of materials which are present in the urine. Although one infer that might water is chemically inert, it must be borne in mind that in a large number of cases there is good evidence of some kind of association between the molecules of the solvent and the solute. Thus, Bayliss cites the fact that one molecule of saccharose takes six up molecules of water, and that in again, glycerol solution exists, to the extent of 99*96 per cent, in a hydrated form. In watery the solution, again, extent to which ionisation takes place is very a condition high, which renders a " mobile possible most chemistry." And, of all finally, common liquids the surface tension of water is only exceeded that of Surface by mercury. tension plays a most important part in the movement of water in a capillary system like the soil, it also an probably plays equally valuable rdle in the changes which take place Its Physiological Significance. 5

4 within both the living plant and animal, as it is the effective agent in the phenomenon known as adsorption or surface condensation, a phenomenon which leads to the all-important uneven distribution of the solutes in a system. The modern interpretation of the rate of enzyme action, for instance, attributes it, in the main, to adsorption. Familiar as is the fluid-water, equally familiar is the chemical symbol which purports to represent its nature. Perhaps no symbols are so widely recognised as H20. To-day, however, it is generally accepted that only under the most limited of conditions can the fluid we know as water be represented by the simple H20 with a molecular weight of 18. It has been pointed out that if this were uniformly the case, the freezing point should be about ?150? and the boiling point ?100?. Actually the common everyday water must be a polymerised fluid in which a number of molecules are united together. The polymers must, of course, be regarded as chemical entities readily convertible one into the other. Such polymerisation would account for some of its properties. An analogous case of chemical or physical change dependent on polymerisation is seen in the case of formaldehyde. Ordinary formaldehyde is liquid at ?20? whereas its polymer of 3 molecules of foi'maldehyde trioxymethylene is solid at 150?. Discussing the fact that the degree of polymerisation of water increases with falling temperature, Bayliss states that " cold water is not the same liquid chemically as warm water and is less volatile, hence its vapour pressure falls more rapidly than that of a simple liquid would. This is a favourable circumstance in regard to the properties of water as a regulator of animal temperature, since the cooling produced by its evaporation is greater the higher the temperature is." As regards these degrees of polymerisation many hold that ice is a trihydrol steam monohydrol H20, and liquid water for the most part dihydrol H20:0H2, but containing varying amounts of the other two polymers according to the temperature. Armstrong, on the other hand, objects strongly to this 6 Prof. E. P. Cathcart?Water:

nomenclature. He maintains that " water itself, it is to be supposed, is a mixture of active and inactive molecules; the active molecules being either simple monad-hydrone (OH2) molecules or hydrone-hydrol (briefly hydronol) molecules

inactive, the closed systems which are formed

by the association unaccompanied by distribution of two or more simple molecules?such as are represented by the formulae ?

Water then can no longer be looked upon in the old-fashioned way as a simple inert fluid of constant composition. One must realise that there are both active and inactive molecules, and it may be that this suggested interplay of molecules may possibly play a role in the organism. All the water which is in the present organism does not come from some source external to the body, but is in part formed in the tissues during metabolism. According to Bottazzi, this internal source accounts for about 16 per cent of the water excreted. Babcock has comprehensively summarised the chief functions of so far as water, living matter is concerned, "to dissolve nutrients and serve as a medium for their distribution, to remove waste injurious products from the cells, to control the within temperature narrow limits by its and in the evaporation, chlorophyll producing plants to supply material for the synthesis of matter." organic The water which plays this protean rdle must be available, under in ordinary conditions, abundant amount. the Although internal metabolic supply may in certain of the stages life-history of both animals and plants, e.g., in bulbs, tubers, seeds, and spores on the one and in hand, animals on the hibernating other, be adequate for the immediate needs, if the loss yet by evaporation is at all considerable an external supply is The vitally necessary. demand the adult for by average water from an external Its Physiological Significance. 7 source is, of course, conditioned by his mode of life. If strenuous work be actively engaged in, then the loss not only by invisible but also by visible perspiration is obvious to all. Atwater and Benedict, amongst others, have determined this daily loss. They found a mean loss, from the average of forty-nine experi- ments on four men, of 935 grams during rest, and, as the following table shows, a very marked rise when work was done:?

Average Loss of Water in Grams. Net Work Rest. Work. Calories.

J-i. V/,j ? ? ? 977 2275 1551

A. W. S., . 859 J. F. S., . 830 1670 1404

J. C. W., . 835 3255 2723 J. C. W. (16 hours' work), 7381 about 6737

A loss of about 7*4 kilograms as the result of sixteen hours' hard work is eclipsed by some of the other reductions in body weight which have been recorded, and which, owing to the relatively short duration of the work, must have been for the most part due to water loss. Thus, losses of 6*4 kilo, in 1 hour 10 minutes of football, 2*5 kilo, in 22 minutes rowing (boat race), and 3 9 kilo, in 3 hours during a Marathon race have been recorded by reliable observers. Quite apart, too, from the marked alteration in water content of tissues which may result from evaporation during strenuous bodily exercise, the normal physiological functioning of the gastro-intestinal tract makes demands of an extraordinary nature which are not generally appreciated. The total turnover of fluid during digestion is literally enormous, amounting as it probably does to about five litres per diem. It is calculated that in the course of the day there is a secretion of from 1,000-1,500 c.cm. saliva, 1,000-2,000 c.cra. gastric juice, 600-900 c.cm. bile, 600-800 c.cm. pancreatic juice, and 200 c.cm. or more intestinal juice. This large volume of fluid is poured into the intestinal tract, where it mingles with the one to two litres of water taken with the food, and yet, apart from the odd 100 c.cm. water which is present in average faeces, it is absorbed into the system. Truly metabolism has its beginning, being, and end in water. That the body has a most marvellous power of dealing with 8 Prof. E. P. Cathcart? Water:

water ingested has frequently been shown. It has long been known that large volumes of fluid may be drunk without any prolonged dilution of the blood, and that contrariwise active sweating produces little or no concentration of the blood. Wilson in my laboratory, for instance, has swallowed 2,400 c.cm. of an isotonic salt solution without increasing his normal output of urine more than about 800 c.cm. He was unable to detect any appreciable dilution of his blood. Engels investigated the problem very thoroughly. He first determined most carefully the normal distribution of water in six dogs, and found that the percentage of water present in the various tissues was wonder- fully constant. He then injected intravenously 0*6 per cent salt solution amount (mean injected being 1,159 grams fluid) into a series of animals (seven in number), and three hours later, having duly noted the total water loss by the kidneys, &c., killed them and examined the tissues as regards their water content. He obtained the following result:?

Percentage or Water Present. Normal Series. Injected Series.

Muscle tissue, . . . 47*74 67*89 Skin 11-58 1775

Rest . . of body, . 4068 14-36

In other words, about two-thirds of the extra water stored in the body were in the muscle and one-sixth in the skin. It is, somewhat perhaps, astonishing that the skin should play such an active part. Possibly?indeed, probably?it is the connective tissue not only in the subcutaneous tissue but also in the muscle that mainly stores the imbibition water. That connective tissue has a considerable very capacity for taking up water, presumably was noted by imbibition, long ago by Chevreul, who obtained some very results on the water interesting absorbing powers of dried connective tissues. to Thus, according Overton, although normal fresh fibrous tissue contained 62 of only parts water, yet dried fibrous tissue could take up nearly 148 of parts water, elastic tissue with a normal content of some 50 cent water per when dried took over 99 and up parts, with some 77 cartilage parts of water took 319 parts when dried. up Of course, it is not implied that more water, any than any Its Physiological Significance. 9 other constituent of living matter, is taken lip indiscriminately, but it is extremely difficult, if not wellnigh impossible, to show that selective action is exercised in living matter when water alone is concerned and, particularly, when dealing with such complex organisms as highly-developed vertebrates. Amongst some of the lower forms of plant life the discrimination which is exercised, even by living matter existing wholly in an aqueous medium, is most beautifully exemplified in a series of analyses of the salt (Na and K) content of four varieties of fucus (as given by Overton) from the same part of the Firth of Clyde, and living under, so far as one can judge, absolutely uniform environmental conditions:?

Salt Percentage. F. digitatus. F. vesiculosus. F. nodosus. F. serratus. Potassium, 22*40 15-23 1007 4-51 Sodium, 8*29 11-16 15-80 21-15 Total asA, 20 04 16-39 16-19 15 63

Thus, although the total ash in these four varieties of fucus varies within comparatively narrow limits, yet the selective action of the tissue cells, living as they do in a watery medium containing the requisite salts in solution, is beatifully shown in the varying balance of the proportions of sodium and potassium. We are forced to the conclusion that just as there is an optimal salt distribution in the tissues there is also certainly an optimal salt dilution. Macallum in his study of palseo- chemistry?whether his conclusions be right or no?did certainly produce some extraordinary interesting evidence in favour of his view that the present composition of blood plasma, in so far as its inorganic constituents are concerned, is probably identical with that of the sea water just before the Cambrian period, and that the salt concentration in protoplasm represents conceivably the salt concentration of the primaeval ocean in which life first appeared. At anyrate, the curious predominance of both potassium and calcium over sodium, which is characteristic of protoplasm, is reflected in the salt relationships in water derived from pre-Cambrian formations. We must now consider the other source of water, viz., the 10 fitoF. E. P. Cathcart? Water:

water which arises by chemical action within the tissues themselves, the so-called metabolic water. During the oxidation of the proximate principles, protein, carbohydrate and fat, there is a production of water which is approximately equal to nine times the weight of the hydrogen present in the original substance. Thus 100 grms. starch containing 6*17 per cent hydrogen yields over 55 grms. water; fat, using the general formula of Hanriot, with 121 grm. hydrogen per 100 grm. material yields nearly 109 grm. water and 100 grm. protein, taking into account the formation of urea as an end product, will yield about 42 grms. water. Incidentally, it may be noted in connection with the high yield of water from fat that one of the characteristics, which has been noted in my laboratory by the several workers who have, for metabolic purposes, been on a purely fat diet, is that " " during the fat period the desire for water almost disappears. The method by which energy is liberated from the foodstuffs to supply the body's needs is by oxidation. As the term the inference to indicates, be drawn, and which, up till recent times has been commonly drawn, is that oxygen is the element mostly concerned in the process. But modern work has definitely shown that the participation of water is essential, and that oxidation may take place in the absence of free Thus Wieland oxygen. has demonstrated that by the use of black in the palladium absence of oxygen, but in the of presence water, carbon monoxide can be oxidised to carbon dioxide at room temperature. The following scheme of events is no mere hypothesis of the chemist, because the intermediate products formic acid, hydrogen peroxide, and hydrogen? have all been isolated :?

The formation of water of is, course, not peculiar to oxidation of the various complete materials, but it may also arise a mere in molecular during change structure, as, for the formation of instance, maltose from or dextrose, during a more complete Its Physiological Significance. ii change in chemical structure, as in the formation of fat from sugar. These changes are perhaps more apparent when stated in formula form :?

As regards the actual yield to the body from the oxidation of an average mixed diet, it has been calculated (Magnus Levy) that each 100 calories of food ingested yields approximately 12 grms. of water. Babcock, who devoted considerable attention to the problem of metabolic water, came to the conclusion that intracellular^ formed water was of greater value to the living structure than imbibed water, as it did not probably bring about drastic osmotic changes. He held that absorbed water had its particular value in facilitating the removal of waste products, but, so far as nutrition went, it might lead to actual starvation " of cells, in that it could cause a movement of nutrients away from rather than towards the points where they are most needed." That an excess of water may lead to starvation of growing cells by washing away nutrients is, of course, most obvious in a simple condition like the ill effects produced by prolonged rain after planting seeds. Babcock, whose main interest lay in the relation of water to seeds, held that, as the production of water during the oxidation of organic material is a necessary consequence of respiration, all viable seeds must contain, at all times, some free water, a fact which has been well established, and that, therefore, a constant production of metabolic water is a sine qua non for the maintenance of the viability of the seed embryo. When growth starts?and an intake of water from without is essential for germination?the demand for, and the production of, water becomes a very characteristic feature. Thus, if the water content of the dried seed be taken on the average as being about 10 per cent, germination begins when the water content has risen to 30 per cent, and, finally, if the growing sprouts be examined, they are found to contain from 80 to 90 per cent water. The high percentage of water in the growing sprouts may be due in part to absorbed water, but, as this is the 12 Prof. E. P. Cathcart?Water:

actively growing ? part, where metabolism is at its height, it may be rightly assumed that the formation of metabolic water is also very active. Whether the role of metabolic water in the cell is different from that of water taken up from without, is a question of great difficulty. As has already been mentioned, there is no doubt that the cells can exercise selective retention in the case of readily soluble salts, and it is equally probable that they can just as effectively control their water movement. It be might suggested, too, that in view of what may be considered an established fact, viz., that wTater may exist in it is at polymeric form, least possible metabolic water may be differentiated chemically from the ordinary absorbed water. If we accept Armstrong's hypothesis that water may be a complex mixture of active and inactive molecules, it is not stretching probability to its limits to suggest also that the water liberated and taken up in the processes of metabolism consists for the most part of the active hydrone or hydronol whereas the forms, circulating?carrier?wrater may be assumed to be mainly in the closed, inactive systems like dihydrone. There is no doubt about the fact that wTater molecules do an play extraordinary active, and so far as human fallible can an judgment determine, apparently absolutely necessary role in the oxidative processes as witnessed, for instance, by the experiments of Wieland already referred to. When we consider the animal kingdom, is there any evidence that metabolic water plays any special part, bearing in mind the statement already made that a mammal will die when it has lost about ten per cent of its water content ? The word mammal must be stressed, because it has been shown that at a low temperature frogs can be dessicated until their muscle contains from only 18 to 26 per cent water instead of the average 79 cent. per Certainly dogs, for instance, can get on water derived along solely from tissue, as Straub found that these animals fed on raw flesh could live without the addition of any further water, if on whereas, fed dry meat powder and fat, four was days the longest over which period they could carry on. Whether animals, if we leave aside for a moment the need for rid getting of the waste could products, manage on their own metabolic water, if losses by evaporation were reduced to Its Physiological Significance. 13 a minimum, is very doubtful, although it has been suggested that such would be the case. Babcock certainly made a good point when he drew attention to the fact that the water requirements of animals whose main nitrogenous waste material is in the form of uric acid are much less than is the case with those which excrete urea, as uric acid is voided solid with a minimum waste of water in contra- distinction to urea which must be got rid of in solution. Many of the lower forms of life like clothes moths,* grain weevils, dry " wood borers, &c., never have access to water, and subsist in every stage of their development upon air-dried food which usually contains less than 10 per cent of water." Presumably in life they are not hygroscopic and do not thus obtain water, because when killed their bodies dry quickly on exposure to ordinary air. The same water-saving value of uric acid is also evident in animals higher up the scale which frequently live in arid regions, like snakes and certain birds. Even the camel does not depend solely on its special physical attributes, such as the possession of a store of fat in the hump, the reduction of evaporation by its special coat, and the possible stomach store of water, for, as recent urinary analyses by Read have shown, there is an even finer metabolic adaptation which must contribute substantially to its capacity to withstand lack of water. The following figures show conclusively how far the special design has been carried :?

of Urine: Nitrogen Content. Urams"ftrams Percentage the Nitrogen. Total nitrogen, 8*70 Ammonia nitrogen, 000 Urea nitrogen, slight trace 0 0 Total creatinine nitrogen, 3-43 39*4 Hippuric acid nitrogen, 3 05 35 1 Purin nitrogen, 1-73 19-9

It is interesting to note that of the three chief nitrogenous products present, creatinine, which forms the bulk of the total nitrogen, is an anhydride compound, and hippuric acid which,

* excreta of the is rich in The clothes moth very purin material and poor in urea. >? 14 Prof. E. P. Cathcart? Water.

as the following formula shows, is a compound of benzoic acid and glycocoll whose formation leads to the liberation of free metabolic water.

And then, finally, there are hibernating animals which subsist during the period of hibernation on metabolic water. Here the special adaptation concerned is the laying down of large stores of fat before the winter sleep begins, supplemented by (a) the reduction of respiration to a minimum ; (b) the lowering of the rate of tissue oxidation; and (c) the state of sleep, all occurring at a low temperature which naturally reduces evaporation from the skin to a minimum. The outline of the tale of water in the organism is then briefly told. It is the very fact of its abundance which has prevented us from appreciating at its true value this wonderful and life- giving fluid. One does not in the end disagree with Rubner's statement that Nature anxiously supervises the maintenance of the water balance, and one can endorse Henderson's dictum that no other substance can claim, however slightly, " to rival water as the milieu of simple organisms, as the milieu interieur of all living things or in any of the countless physiological functions which it performs either automatically or as a result of adaptation."