104 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



FIBRILS. 

 COLLAGENIC FIBRILS. 



Meves's own work (1910a, ]:>. 164) on the histogenesis of collagenic fibrils may 

 now be briefly mentioned. His material consists of a series of preparations of the 

 growing tendon in the posterior extremity of chick embryos of from 6 to 19 days' 

 incubation. He fixed the embryos in a modification of Flemming's fluid, cut some 

 of the specimens in transverse, others in longitudinal sections, stained them with 

 iron hematoxylin, and counterstained with acid fuchsin. In this way the mito- 

 chondria were colored black and the fibrils red. 



The illustrations of the preparations on which he l:)ases his contention are 

 beautifully shown in his second plate (Tafel III). They are arranged in two 

 series of increasing grades of differentiation, the uppermost of which is taken from 

 longitudinal sections and the lower from transverse sections. They show that the 

 mitochondria become accumulated in the peripheral parts of the cytoplasm in 

 stages during which the collagenic fibrils first appear. The mitochondria are fila- 

 mentous, but are not so long as the primitive fibrils, the ends of which he was 

 unable to observe. The figures show, in addition, that there is a decrease in the 

 number of mitochondria in the cells of later stages and that the mitochondria are 

 no longer most abundant in the peripheral parts of the cell. Meves's line of rea- 

 soning is instructive. He says (p. 164) : 



"Was nun die Deutung der beschreibenen Bilder anlangt, so bleibt meiner Meinung 

 nach nichts anderes iibrig, als anzunehmen, dass die Bindegewebsfibrillen aus Chondrio- 

 conten hervorgehen. Die Chondrioconten werden zunachst epicellulJir. Sie andern dann 

 ihre chemische Beschaffenheit, indem sich ihre Substanz in eine solche umwandelt, welche 

 weder durch Eisenhametoxylin noch durch Fuchsin farbbar ist. Auf diesem Stadium 

 treten diejenigen von ihnen, welche in einer Reihe liegen, untereinander mit ihren Enden 

 in Verbindung. An der Bildung einer Fibrille deteiligen sich zahlreiche Zellen (alle die- 

 jenigen, denen ihr Verlauf fest anliegt), indem jede einen Fibrillenabschnitt liefert. Die 

 Fibrillen andern dann zum zweiten Mai ihre chemische Beschaffenheit, indem sie eine 

 intensive Farbbarheit fiir die CoUagenfarbstoffe gewinnen. Schliesslich werden sie von 

 den Zellen frei und kommen in den Spaltraumen zwischen ihnen zu liegen." 



Before we enter upon a criticism of Meves's work it is necessary for us to 

 recognize, in all fairness, that he does not claim to have conclusively established 

 the transformation of mitochondria into collagenic fibrils, since, as he himself empha- 

 sizes, the steps which lead up to this conclusion consist of assumptions as well as of 

 positive evidence. It is important above all to note that, according to Meves, 

 the mitochondria (chondriocontes) are invisible, not staining with either iron 

 hematoxylin or fuchsin when they form the fibrils. This assumi)tion that they 

 are invisible when the most important stage of the whole process is taking place 

 disarms all criticism at the outset. 



Meves makes his chain of evidence ("Kette der Beweise," p. 165) still more 

 fragile by asking the question : " If the chondriocontes have nothing to do with the 

 formation of fibrils, why then do they become epicellular?" I do not know whether 

 Meves means by the term "epicellular" that the mitochondria are actually out- 



