THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 103 



in addition to the phospholipin, of an albuminous substratum of some sort. Nev- 

 ertheless, in the vast majority of cases a true transformation is out of the question. 



The idea of a transformation is often based upon the mere observation of sub- 

 stances within the mitochondria. The fallacy of this line of reasoning is evident, 

 for no one would say that because the cell contains iron or phosphorus the iron or 

 phosphorus is produced by a transformation of the substance of the cell. Sub- 

 stances unquestionably penetrate into the mitochondria from the cytoplasm, as 

 shown by the fact that in these supposed transformations of mitochondrial mate- 

 rial into something else there is always a distinct increase in size. For instance, 

 the mitochondria possessing bleb-like swellings in gland-cells are larger than those 

 without them, and mitochondria containing starch, fat, pigment, crystalloids, 

 and other materials are invariably greatly enlarged. In cases where granular 

 mitochondria expand to form vesicles careful observation will often show that there 

 has been little or no change in the absolute amount of mitochondrial substance; it 

 has simply become spread over a larger area. We may safely regard this imbibi- 

 tion from the cytoplasm as establishcxl, but how the materials are taken in is exceed- 

 ingly difficult to explain. It differs sharply, however, from the normal process 

 of growth because the expansion is lateral, while in growth extension is usually 

 longitudinal (p. 70). I incline strongly toward Regaud's eclectosome theory (IQOOa, 

 p. 919), according to which mitochondria play the part of plasts choosing and 

 selecting substances from the surrounding cytoplasm, condensing them and trans- 

 forming them in their interior into infinitely diverse products; but I would venture 

 to emphasize the fact that in all this the mitochondria may be acting in an entirely 

 passive manner as a vehicle, taking up materials by virtue of their phospholipin 

 constitution, or on account of physical forces acting on their surfaces, or for other 

 reasons, and that the optically homogeneous ground-substance of the cytoplasm 

 may be the active and essential agent in this as in so many other vital mani- 

 festations. No change of the mitochondrial substance need be involved. Sugar, 

 which is heaped uji in i^lasts, is certainly not formed through a transformation 

 of mitochondrial material, or of the plasts which contain it. They merely 

 act as containers, the foreign material being localized in certain regions of the 

 filament. 



But in rare cases there is evidence of an actual change in the mitochondria 

 themselves, especially in the formation of fibrillar structures, in cornification, and 

 in other similar processes. We may conceive of this as taking place in several 

 ways: (1) by the addition of substances from the cytoplasm which enter into 

 close combination and become integral constituents of the mitochondria; (2) by 

 the mitochondria giving up to the cytoplasm certain of their normal constituents; 

 (3) by chemical dissociation which may or may not be followed by resyntheses. 

 Fat, lipoid, and other similar substances might be formed; but it is imj^ortant to 

 bear always in mind that the po.ssibility of a transformation diminishes in direct 

 proportion to the degree of dissimilarity between the mitochondria and the material 

 in question. It is for this reason that I am willing to entertain almost any alterna- 

 tive hypothesis rather than accept unqualified statements of the chemical trans- 

 formation of mitochondria into dissimilar substances. 



