THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 105 



side the cells, lying upon them, or that they are simply accumulated in the periph- 

 eral parts of the cytoplasm within the cell-membrane. The derivation of the 

 term and the appearance of certain mitochondria illustrated in his figure 25 seem 

 to support the first interpretation. The difficulty of asserting that mitochondria 

 in Meves's preparations are without the cell-wall is great, not only because the cell- 

 walls are not differentially stained, but also by reason of the mode of deposition of 

 collagen. It seems, therefore, that what Meves describes is simply a heaping-up 

 of mitochondria in the cytoplasm beneath the cell-membrane. 



A similar peripheral arrangement of mitochondria in the cytoplasm has been 

 described in a whole host of conditions other than fibril formation and therefore is 

 without special significance in this connection (see p. 76). 



The filamentous shape of the mitochondria might at first sight appear to be 

 indicative of a transformation into collagenic fibrils. This is, however, not the 

 case, because mitochondria, which are also thread-like, occur in the same stage 

 of development in cells which do not form fibrils. 



Meves's other argument that the mitochondria decrease in number as the 

 fibrils form in the course of development would be valid only could it be shown 

 that the diminution in number was not brought about in some other way. In- 

 deed, it is only one instance of a very general phenomenon, that the mitochondria 

 grow fewer and fewer in all cells as they grow older. Meves, himself (1911a, p. 495), 

 has shown this to be the case in the later stages of the cytomorphosis of red blood-cells 

 of the guinea-pig; Firket (1911, p. 544) has demonstrated the same phenomenon 

 in the cells of the egg tooth of chick embryos; and Regaud and Favre (1912, p. 328) 

 have confirmed his results by their observations on the epidermis of man. 



Meves's hypothesis of the role of mitochondria in connective-tissue fibril 

 formation can not, apparently, be reconciled with Baitsell's (1916, p. 754) recent 

 work on wound healing. Baitsell discovered that certain fibrils form, quite apart 

 from the cells, as a differentiation of a typical fibrin net in the coagulation tissue 

 between the cut surfaces. The cells all wander in later. The staining reactions 

 of the new fibrous tissue, formed in this way, appear to resemble in many ways those 

 of true connective tissue. Here we are dealing with the formation of fibrils Uke 

 those of connective tissue from a known substance, fibrin, iii the absence of cells, 

 and, since the mitochondria are alwa^^s intracellular, it is inconceivable how they 

 could be bodily transformed into the fibrils, as Meves claims. 



It is interesting also to note that M. R. Lewis (1917, p. 56) has made a care- 

 ful study of the behavior of mitochondria and fibrils in cultures of subcutaneous 

 tissue of chick embryos. The fibers in the explanted piece were not observed to 

 grow either in length or bulk, but new fibrils arose as delicate lines in the exoplasm 

 of the cells and quite independently of the mitochondria. The cessation of growth in 

 the one and the initiation in the other may indicate some superficial, or perhaps 

 fundamental, difi"erence. No attempt was made to compare the microchemical re- 

 actions of the new-formed fibrils with the definitive connective-tissue fibrils in the 

 organism. The observations indicate the independence of mitochondria and afford 

 a plausible alternative hypothesis of the development of connective-tissue fibrils. 



