440 NATURE [SEPTEMBER 24, 1927 sheep and oxen appear to contain about 200 times tho Letters to the Editor. amount of vitamin A found in the best butter [The Editor does not hold himself responsible for examined." Without entering into a calculation of opinions 53xpressed by his correspondents. Neither the available supply of liver,- we may assume that can he imdertake to return, nor to correi;pond with Great Britain's need is easily met at home, supple­ the write·rs of, rejected manuscripts intended for thill mented if necessary by Empire produee. It may be or any other part of N ATURF:. No notice is taken stated that the vitamin content of the fat obtained of anonymous communications.] from imported New Zealand liver equalled that of the liver of home-killed animals. The Sources of Supply of Vitamins A and D. As an additional advantage for the purpose m1g­ THE problem of an adequate supply of the fat- gestecl, we find that these fats are freo from the soluble vitamins for the needs of the growing popula­ objeotional flavour of fish oils, which is apparently tion has received prominent attention at the recent connected with the presence of the highly unsaturated meeting of the British Association. The shortage in clupanodonic acid (C 22H 340 2 ) and the Fearon colour the supply of milk fat in particular was emphaR-ised, reaction (Biochem. Jour., 1342; 1926). Owing to their and a simple calculation led to the conclusion that low melting-point, liver fats can be ea,;ily incorporated this shortage is not a local one in Great Britain, but with other fats, such as margarine. Although easily of world-wide extent. Butter is irreplaceable by mar­ extracted by the use of fat solvents, their isolation garine as long as this article of diet is defioient in would probably not be necessary in large scale manu­ vitamins. .1£ven if we do not share the gloomy view facture. Vitamin A, being fat-soluble, can be directly as to the effect of this shortage on the health of the extracted from the tissue by a neutral oil. The well­ nation, since milk fat is not their only source, it must known skill of the margarine manufacturer should be admitted that the problem of the supply of fat. enable him so to incorporate the liver fats with hiR soluble vitamins is of outstanding importance. product as to convert a dietary artiele, already We would like to direct attention to the outcome of iclent,ical with butter in calorific value, into a cheap recent researches, only partially published as yet, in and palatable product of equal biological efficiency, so tho course of which we became aware of easily access­ far as vitamin A is concerned. ible sources of both vitamins A and D. The solution The no less important vitamin D, another variable of the problem dopends now onl~• on the industrial constituent of butter, remains to be considered. Con­ application of the knowledge made available by such trary t,o the expectation that this would also be con­ research. tained in the mammalian liver fat, we found that the So far as vitamin A is concerned, we found that tho liver fat of sheep, at any rat,e, is practically devoid of chromogen responsible for the arsenious chloride this vitamin. It would seem that, unlike fish, the colour reaction, discovered by one of us (0. R.), is herbivorous mammal does not store vitamin D in the present not only in the liver of the cod, but also in liver. On tho other hand, the body fats of certain the livers of all animals examined, fishes, birds, and fishes, although free from vitamin A, as t,estecl both mammalR. A Rtucly of the quantitative distribution colorimetrically and biologically, were found t,o bo a of this chromogen and its correlation with vitamin A good source of vitamin D. An interesting exception by means of the biological growth-test (Lancet, ii. 806; to what appears to be a general rule was revealed in 1926), proved that the amount present in other liver the examination of the body oil obtained from eels. fats in many cases far exceeds that found in cocl-livor The oil content of this fish is relatively high (about oil, the richest source of vitamin A previously known. 30 per cent.), and it contains not only vitamin D, but It must be remembered that the main reason for the also vitamin A in an amount nearly equal to that of selection of the cod as a source of medicinal oil, leading Romo Norwegian cod-liver oils (tested colorimetrically to the development of the cocl-livor oil industry, was and controlled by the animal test). This result oon­ the extraordinarily high fat content of the cod's liver finns, incidentally, the high value empirically attri­ and its relatively easy extraction on a commercial buted to the eel as an article of diet. scale. As regards vitamin A content, however, we There is, however, no need to search any longer for found that the liver oils of other fishes, such as salmon a natural source of vitamin D, since we a're now able or halibut, are often more than 100 times as rich as to produce this important vitamin artificially by cod-liver oil. irradiation of ergosterol (Biochem. Jour., 389; 1927). On account of U1eii: limited accessibility, these oils Irradiated ergosterol possesses extraordinarily potent cannot be considered as a commercial source of anti-rachitic activity, J /10,000-1/20,000 mgm. pe1· vitamin. Tho ,;ame reason excludes the liver fats of diem prnventing and curing rickets in rats. Clinical birds, some of which, sueh as those of the grouse, experience has since shown that human rickets al,;o iR goose, fulmar petrel (Biochem. Jour., 111; 1927), are rapidly cured by daily closes of 2-4 mgm. The amount extremely potent. The liver fats of herbivorous mam­ to be incorporated with margarine need, therefore, be mal°', on the other hand, appear to be an ideal source only extremely small. By a- study of the best condi­ of vitamin A. These animals live mainly on green tions of its fonuaUon in yeast, a practically unlimited fodder, the original source of vitamin A, and accumu. supply of ergosterol should be available for this late a store of it in the liver, as do fish and birds. purpose. We found by both colorimetric and biological tests The margarine manufacturers have therefore at that tho liver fats of :::hec:p, calf, and ox contain on their disposal, if they care to make use of them, means the average as mueh as ten t,imes the amount of which should make a perfect biological ,mbstit,ute for vitamin A as a good Nowfounrlland cod-liver oil. butter accessible, wit,hout, unduly raising the price of Taking the vitamin A content of butt,er-a ve1·y margarine. Moreover, by carefully controlled methods variable factor-as from 1/20 to 1/100 that of cod-liver of manufaeturc, it should be possible to supply a oil, those fats may be said to be from 200 to 1000 times product of constant vitamin content, superior in this more potent in this respect than butter. A recently respect to natural butter, the vitamin content of published letter (see Times, Sept. 7) shows that by an which depends on too many uncontrollable factors of interesting coincidence our results in this respect are the food supply of the cow. 0. ROSENHEIM. confirmed by the independent observations, hitherto T. A. WEBSTER. not published in detail, of Prof. Wilson, formerly of National Institute for Medical Research, Cairo. According to these, "the liver fats of Egyptian Hampstead, N.W.3, Sept. 13. No. 3021, VoL. 120] ©1927 Nature Publishing Group.