MITOCHONDRIA VARIATIONS IN NERVE CELLS 339 



has been able to alter the form of his artificial mitochondria, 

 made out of lecithin, by varying the physico-chemical proper- 

 ties of their environment. Since there is a general concensus of 

 opinion in favor of the view that mitochondria are a combina- 

 tion of lipoid and albumin it is possible that alkalinity or acid- 

 ity would affect their form. The acidity acting upon the pro- 

 tein fraction might cause it to become hygroscopic and to swell 

 (Cowdry '16b, p. 440). The fact that the Nissl bodies, as well 

 as the mitochondria, are often larger in the peripheral cyto- 

 plasm than they are in the .immediate vicinity of the nucleus, 

 would seem to indicate that some common environmental fac- 

 tor may be operating in the case of both, notwithstanding the 

 fact that the Nissl bodies are probably a coagulum or a pre- 

 cipitate resulting from fixation. 



In a general discussion of this kind the mechanical factors 

 which sometimes operate, in the surrounding fluid, in shaping 

 the morphology of mitochondria must not be lost sight of. 

 Thus N. H. Cowdry has observed the changes in the form of 

 mitochondria in the streaming protoplasm of living plant cells. 

 He has seen straight filaments assume the form of loops and 

 spirals in response to currents and eddies in the stream, indi- 

 cating clearly that they are flexible and that their form is in a 

 measure determined by their environment. Conditions of pro- 

 toplasmic stress and strain, occurring especially in the course of 

 development, probably influence the form of mitochondria also. 

 In the outgrowing nerve fibers, for instance, the mitochondria 

 are generally filamentous. Whether mechanical factors of this 

 sort may play any considerable role in determining the form of 

 mitochondria in adult nerve cells is unknown. It is highly prob- 

 able that some combination of the two factors of variation in 

 internal composition and of changes in the surroundings are 

 mutually responsible for the variations in form observed. 



Bearing upon doctrine of neurone specificity. These observa- 

 tions on variations iij the morphology of mitochondria bring to 

 light another specific difference between the internal structure 

 of nerve cells of different categories; for it has already been 

 pointed out that these differences in the form of mitochondria 



