68 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



Filamentous mitochondria with bleb-like swellings are to be found in some secret- 

 ing cells, but not in all. The blebs are supposed to be the precursors of secretion. 

 In plant cells, starch, pigments, and other materials are unquestionably laid down 

 in them, while in animal cells they are said to give rise to granules of zymogen. 

 Many cells which form a definite secretion (plate 1, figs. 3 and 7) do not possess 

 mitochondria armed with these swellings. I refer also to mucous cells. On the 

 other hand, while filamentous mitochondria are exceedingly common, they never, 

 to the best of my knowledge, have blebs in cells which do not form some distinct 

 secretion. I have in mind particularly the nervous system, where mitochondria of 

 this kind are unknown. The swellings are certainly not the result of technique; 

 they represent a reaction on the part of mitochondria to some definite and specific 

 demand or condition of the cell. 



In other localities mitochondria are rod-like. They vary in length and in 

 girth. They are long and very straight in the cells of the convoluted tubules of 

 the kidneys, where they apparently constitute the well-known batonnets of Heiden- 

 hain. Here also they are of very large diameter. vSmaller rod-like mitochondria 

 are often to be seen in muscle-cells between the fibrils, in some nerve-cells, in fact 

 in almost all tissues. Sometimes a swelling will develop at one end of a rod and in 

 this way a pear-shaped mitochondrion will be formed. Occasionally they are formed 

 through the action of the fixative upon mitochondria of the filamentous variety. 

 The fixation may also modify their size to a certain extent; it may cause them to 

 swell or to shrink, so that we must be on our guard. 



Granular and dumb-bell-shaped mitochondria are of very common occurrence, 

 though they are not so widely distributed as the filamentous and rod-like forms. 

 They are quite spherical and resemble cocci rather than bacilli. It is sometimes 

 diflficult to distinguish between them and other cell inclusions on this account, 

 because these other materials occur in the form of droplets also, rarely if ever as 

 rods or filaments. Mitochondria of this variety are very abundant in some egg-cells 

 (plate 1 , fig. 6) . The absence of very minute granular mitochondria merging into the 

 invisible is of interest from the point of view of an origin de novo through condensa- 

 tion (page 98). The dumb-bells are usually interpreted as stages in the division 

 of single granules, but it is unnecessary to say that they may equally well represent 

 an approximation of two originally separate granules. Some fixatives will cause 

 filamentous mitochondria to break up into granules, and I have even known janus 

 green to bring about this change. Good fixatives which have poorly penetrated 

 the deeper layers of pieces of tissue regularly cause this granular degeneration of 

 mitochondria, so that the mitochondria become filamentous and gradually assume 

 their normal condition as one approaches the periphery of the block. 



Mitochondrial networks are of comparatively rare occurrence, though they are 

 found normally in certain types of cells. They have been described in sper- 

 matogenesis, the Lewises (1915, p. 356) have seen them in tissue cultures, and I 

 have occasionally seen them in the acinus cells of the pancreas of mice stained with 

 janus green. They are of variable extent. They may consist of one or two meshes 

 or of several. They are often, though not always, arranged about the nucleus. 



