THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 67 



There is a tendency among investigators to l:)elieve that filamentous mito- 

 chondria are the direct result of streaming movements in the cytoi)lasm. Certain 

 cases may be cited in support of this theory, like the outgrowing nerve-fiber, for 

 instance, in which the mitochondria are always filamentous. In gland-cells also 

 they are usually filamentous and stretch from the basement membrane toward the 

 lumen in the direction of the passage of materials from the blood-stream into the 

 gland-ducts. Again, in dividing cells, the mitochondria often stretch out in the 

 direction of separation. But we have other cases, which demand explanation, in 

 which the mitochondria are rod-Uke or even granular, in spite of the streaming 

 movements; and still other cells where the mitochondria are filamentous, though 

 the cytoplasm is to all intents and purposes stationary, or at any rate as motionless 

 as it ever is. Thus, the mitochondria are granular and rod-hke, not filamentous, 

 in living human polymorphonuclear leucocj'tes during amoeboid movement and in 

 the streaming protoplasm of certain plants. On the contrary, in sharp contrast 

 are cartilage-cells and bone-cells, where, so far as we know, the cytoplasm is rela- 

 tively quiescent, yet the mitochondria are filamentous. They remain thread-like 

 in the nerve-fiber throughout the whole life of the animal, even though there is no 

 longer a pushing-out of substance. Nicholson (1916, p. 332) has found that they 

 are constantly filamentous in the bodies of some nerve-cells, granular in others; 

 and that where they are filamentous they are more so in the peripheral cytoplasm 

 (where they are disposed parallel to the cell-wall) than in the deeper cytoplasm 

 about the nucleus. If their shape is conditioned by protoplasmic streaming, our 

 conclusion must be that some types of nerve-cells constantly exhibit it, that others 

 never do, and further that the little vortices are most powerful in the peripheral 

 cytoplasm, where the mitochondria constitute a clue to their direction. And this 

 is not the end of the interesting deductions which would follow. While some 

 workers are inclined to pin their faith in the real existence of such currents in nerve- 

 cells. Kite's' microscopic dissections with very fine glass needles have brought to 

 light the fact that their cytoplasm is very viscid and has the physical consistency 

 of a gel. Furthermore, Key's'- observation that it is difficult to alter the distribu- 

 tion of cytoplasmic materials in nerve-cells by centrifuging indicates the improb- 

 ability of any considerable protoplasmic streaming. 



Rubaschkin's (1910, p. 428) idea that filamentous mitochondria are char- 

 acteristic of specialized cells and granular ones of embryonic, undifferentiated 

 cells has been negatived again and again; and Dubreuil's (1913, p. 137) view that 

 filamentous ones are indicative of rest and granular ones of rapid multiplication 

 by division is not borne out by recent work. According to the descriptions of 

 Moreau (1914b, p. 538) they are granular in the spores of the fungi in which the 

 cell activities are at a very low ebb, and X. H. Cowdry finds that they are filament- 

 ous in the more or less inactive cells of the radicle of the dried seed pea. We have 

 here two instances of mitochondria in quiescent protoplasm; in one they are granular 

 and in the other filamentous. Numerous other instances might be cited to show 

 that filamentous mitochondria are not indicativ e of rest. 



' Public lecture at the Marine Biological Laboratory. Woods Hole. ' Personal communication. 



