THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 77 



chondrial continuity. A very careful study made by N. H. Cowdry, in this labora- 

 tory, of mitochondria in the streaming protoplasm in many varieties of plant-cells 

 (where they may be easily followed unstained) failed to reveal any indication of 

 independent motility on their part. True, they dart from place to place in the 

 cytoplasm, but this may in almost all cases be referred to definite currents and 

 eddies in the stream. Moreover, I have examined mitochondria vitally stained 

 with janus green in human polymorphonuclear neutrophile leucocytes during 

 amoeboid movement and phagocytosis and I have likewise failed to detect any sign 

 of independent motility. The movements can not, however, be entirely explained 

 away on the basis of currents in the cytoplasm, because we have no reason to sup- 

 pose that such currents exist in the egg-cells. They seem to be almost purposeful. 

 They are entirely different from Brownian movement, though the mitochondria do 

 exhibit true Brownian movements when the cells take up water and when the 

 balancing action of bombarding molecules is upset. The consistency of the cyto- 

 pla.sm has little to do with it, because peripheral condensations occur in nerve- 

 cells as well as in egg-cells; in nerve-cells the cytoplasm is very viscid, in egg-cells 

 very fluid. The mitochondria may be easily thrown down with the centrifuge in 

 egg-cells, but not in nerve-cells. 



It may be a question of adsorption. The Gibbs-Thomson principle tells us 

 that any process which diminishes free energy at an interface will tend to take place. 

 Now, the mitochondria are nothing less than minute particles of lecithin-hke ma- 

 terial in suspension, and we know that hpoids decrease surface tension, so that we 

 would naturally expect them to be heaped up at the nuclear and plasma membranes; 

 but it is difficult to explain their active migration to and fro. Perhaps we are deal- 

 ing with electrical adsorption. The mitochondria may carry a charge, but no 

 adsorption could take place without the presence of a charge of the opposite sign 

 upon the nuclear or plasma membrane, as the case may be, and of this we have no 

 information whatever. Here again the movements backward and forward are the 

 stumbling-block. 



There is one more point for which a tentative explanation may be advanced. 

 It will have been noticed "that in animal cells rather more variations seem to be 

 met with in the arrangement of mitochondria than in plant cells. This may be 

 correlated in some way with the fact that animal cells are more generally polarized; 

 I mean polarized for irritability, conduction, secretion, contraction, and so forth, 

 properties which do not play so great a role in the life of plants where separate 

 regions of the cell are not so distinctly marked off.''^ The division of labor among 

 animal cells is greater than in plants. They have to perform a great variety of 

 functions under different conditions, so that in a single animal there is far greater 

 diversity of organization among its cells than in a single plant. This the mito- 

 chondria reflect. 



From a practical point of view it is a very simple matter, with comparatively 

 little experience, to tell by the inspection of a cell whether the distribution of mito- 

 chondria within it differs from the normal, and this is another indicator of cell 

 activity and of cell injury which has received but scant attention. 



IN. H. Cowdry, 1917, p. 215. 



