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On the Formation of the Ground Substance of Loose Connective Tissue by G

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On the Formation of the Ground Substance of Loose Connective Tissue by G On the Formation of the Ground Substance of Loose Connective Tissue By G. Iasswoin. (Laboratory of Experimental Histology and Biology (Prof. A. Zawarzin), State Roentgenological, Radiological, and Cancer Institute, Leningrad.) With Plate 10. THE formation of the ground substance of connective tissue has for long been one of the most controversial problems of histology. In spite of the diversity of the material studied, and of the methods of investigation used, there exists on this problem as yet no generally accepted view. Thus, we have at present several theories treating differently of the process of the forma- tion of the ground substance and of its fibres. Ever since the theory according to which the collagen fibres1 are considered as proceeding from an immediate trans- formation of cytoplasmic structures, such as the fillar mass and the chondriosomes (Flemming, Eeinke, Spuler, Meves) has been discarded, the said problem has been reduced to the study of the formation of the amorphous substance in which and from which the fibres originate. Since the amorphous substance was recognized to be the product of cell activity its formation might be supposed to occur either by way of secretion or by transforma- tion of the protoplasm. On the theory that the amorphous substance arises from cells by secretion (Merkel, v. Ebner, Petersen, Plenk, and others) the origin of fibres from this substance is considered certainly not as a phenomenon occasioned by endogenous formational potentialities of the protoplasm, but as a result of mechanical relations and forces acting upon the amorphous substance pro- duced by the cells; in this lifeless amorphous substance the 1 The problems concerning the elastic fibres are not included in the present study, which deals only with collagen fibres. NO. 310 T 272 G. IASSWOIN fibres are formed under the influence of ' pressure and tension' (Zug und Druckspannung, Eoux). From the point of view of the authors adhering to the theory of the transformation of protoplasm (Hansen, Studnicka, Mall, Laguesse, Schaffer, Zawarzin, Hueck, Wassermann, and others) the process of formation of the ground substance takes another course. According to them, the fibres do not originate directly from intracellular formations, nor may they be considered as a simple product of cellular secretion. In the primary stages of develop- ment the fibres originate from the protoplasm lying in the peri- phery of the cell, from the so-called ectoplasm. What remains of this ectoplasm after fibre formation represents the amorphous 'cementing' substance (Kittsubstanz) that lies between the fibres. From this point of view the ground substance (meta- plasm), fibrillar as well as amorphous, while losing in the course of the next developmental stages its direct connexion with the cells that have changed into pure endoplasmic elements, retains nevertheless a certain minimum of vital properties; thus it is capable of further quantitative accretion and production of fibres independently of the cells. In other words, it is capable of so-called 'formative activity'. Thus the ectoplasmic theory admits of two ways of formation of the ground substance—in early stages it is produced at the expense of the ectoplasm, while in subsequent stages it is increased by its own metabolism. Besides the theories cited there exists another theory (Na- geotte) which generally denies the existence of amorphous ground substance of a particular character. According to this theory the fibres are contained directly in the colloidal inter- stitial liquid, from which they originate, in the case of fibrin, under the influence of a certain hypothetical ferment secreted by the cells; at the same time it is to be understood that the fibres are not possessed of any vital property. This theory is particularly supported by the authors who have studied the formation of fibres in tissue cultures. Thus, for instance, Baitsell came to observe in cultures the formation of fibres from nutritive plasm and fibrin. In respect of tissue cultures Baitsell's opinions have been refuted by Chlopin. To begin with, the latter author has observed the formation of fibres in areas CONNECTIVE TISSUE 273 of the explant containing no fibrin. Considering the experi- mental conditions used by Chlopin, it would further have been necessary to admit that human mesenchymal cells evoke the formation of fibres in the plasm of the chicken embryo, i.e. in a foreign plasm—which from the point of view of biology seems hardly possible. It would be more correct to admit, as Chlopin remarks, that the fibres originate in a substance that in some way is produced by the cells of the tissue culture. However, for investigators who consider the formation of fibres to be a solely physico-chemical process, these considerations are scarcely convincing. A comparison of the above-mentioned theories concerning the formation of the ground substance leads to the conclusion that, at least in respect of the early stages of development, only the theory of the transformation of protoplasm, i.e. the ectoplasmic theory, rests on proofs based on direct observations (though not all the investigators consider these proofs as equally convincing). The secretory and fermentative theories are entirely bereft of such proofs; they are solely based on hypotheses and exclusions of other possibilities owing to the lack of facts. Concerning the secretory theory it is necessary to point out that the authors supporting it never speak directly of secretion, but describe the process by means of which, according to them, the ground substance is produced as a 'segregation' (Aus- scheidung, Abscheidung, Absonderung). They do not speak of secretion because, as a matter of fact, judging by the descrip- tions given, they never observed secretion; they just saw that a certain substance in which the fibres arise appears about the cells, that it seems to be produced, 'segregated', by them. As the supporters of the ' segregation' theory have not discovered either secretion or an immediate transformation of cellular proto- plasm into the said substance (which the supporters of the theory of the transformation of protoplasm designate as ecto- plasm), and as they wish to state that this substance is produced by certain cells,1 they prefer to use a neutral expression, 'segregation', that, properly speaking, explains nothing. In this 1 The word 'cell' is here equivalent to the endoplasm of the 'eeto- plasmists'. 274 o. IASSWOIN respect certain authors (Petersen, Plenk, and before them v. Ebner) entirely change the point under discussion. They say that, as a matter of fact, there is no difference whatever between transformation of the protoplasm and secretion, and that the discussion is one merely of words. Thus, according to Petersen: " Jede Secretion kann eine Umwandlung genannt werden, denn die Materie, die spater als Sekret erkennbar wird, steckt vorher in der Zelle, ist ein Teil des Protoplasten. Die geringere oder grossere Geschwindigkeit in der Erganzung des verbrauchten Materials ist es, die den Vorgang unter Umstanden als Um- wandlung von Zellteilen erscheinen lasst, nahmlich ob der Protoplast daher an Grosse abnimmt oder nicht. Die lebende Substanz vollzieht in alien Fallen eine Synthese, leitet sie wenigstens ein, und von einer Umwandlung sollte man nur dann reden, wenn vom Protoplasten nichts, d.h. kein regenera- tionsfahiges Gebilde iibrigbleibt." As a matter of fact, even leaving out of consideration that the product of secretion is accepted as dead substance, while transformed substance is reckoned to retain to a certain degree the character of a live substance—even in this case, the discussion is not solely one of words. Such would indeed be the case if the physiological part of the process alone were discussed, as from this point of view it is really hardly possible to distinguish between secretion and transformation of the protoplasm; or if it were previously established and known that the ground substance is produced by certain cells; or, finally, if there did not exist a theory, according to which the cells really secrete, not the ground substance, but the ferment under whose action collagen fibres arise from the interstitial liquid. As a matter of fact the cir- cumstance that ground substance is produced, 'segregated', by cells and withal by one kind or other, remains yet to be proved; and this of course requires an indication of the mode, of the form of this 'segregation', because the expression 'segregation' (Abscheidung) without this has no meaning whatever. Three forms of secretion—the mero-, apo-, and holocrine—are known to us. If the adherents of the 'segregational' theory were able on the strength of their investigations to affirm that the process of' segregation' takes the form of an apo- or holocrine secretion, CONNECTIVE TISSUE 275 their observations would to a certain degree coincide with the data of the ectoplasm theory. But they are not able to make such an affirmation, because according to their descriptions and illustrations the cellular protoplasm and the ground substance are always distinctly demarcated from each other. As to the merocrine secretion, this form has been observed, to my know- ledge, only by Eenaut and Dubreuil.1 However, Dubreuil, for instance, abstains from giving an opinion as to whether the product of this secretion is represented exactly by the ground substance itself or by some ferment acting on the interstitial liquid, and, consequently, he gives no definite answer to the question concerning the formation of ground substance. Thus the discussion on ' secretion or transformation of cellular proto- plasm ' is by no means a simple discussion of words—it is con- cerned with the way in which the cells take part in the formation of the ground substance, and also further with the question what cells exactly participate in its production.2 1 According to v. Korff odontoblasts and osteoblasts possess secretory granules. The author supposes that these cells produce by way of secretion (merocrine) a special matter that gives to the ground substance the capacity of retaining calcium salts.
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