74 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



along in the metamorphosis show no evidences of polarity and contain mitochondria 

 scattered uniformly throughout the cytoplasmic area. In the thymus gland the 

 cells are unpolarized and the mitochondria are not arranged in any definite way. 

 The so-called " rhagiocrine " cells of Renaut are unpolarized and contain mitochon- 

 dria quite uniformly distributed. Other instances might be cited. We must 

 regard secretion as a fundamental property possessed by all cells. Where they 

 speciaUze in it, and give up all their energies to it, and retain their primitive connec- 

 tions with the basement membrane, the polarity is the most pronounced and the 

 arrangement of the mitochondria the most striking. It is hard to say whether, 

 when cells become depolarized (if they ever do), the mitochondria lose their polar- 

 ized arrangement and become distributed uniformly. This has a very definite 

 bearing upon the problem of the relation of mitochondria to polarity in gland- 

 cells. It would seem that the carcinomata would constitute favorable material, 

 because in some of theni the secreting cells lose in a measure their power to secrete 

 and often with it their polarity and take on unusual powers of multiplication. At 

 such times one would expect the mitochondria to become redistributed uniformly 

 throughout the cytoplasm. 



In plants secreting cells are not so generally polarized and the ones which are 

 polarized have not been investigated, so that we can obtain no help in this direction. 



Child's (1915, p. 202) view that, in general, polarity is dependent upon the 

 axial gradient in metaboUsm, considered with the likelihood that mitochondria 

 themselves pro])ably play some part in metabolism, is perhaps not without signifi- 

 cance. There may be some relation here, and there may not — we can not tell. 

 Tashiro (1915, p. 112) has established, by measurements of the CO-, output, a 

 gTadient in metabolism of the nerve-fiber which corresponds with the polarity of 

 the nerve-cell. I have diligently searched in nerve-cells of many forms for some 

 relation between the distribution of mitochondria and dj'namic polarization and 

 have failed to find any. The polarity of egg-cells— that is to say, the plane in 

 which cleavage takes place — ^is apjmrently not related to the arrangement of mito- 

 chondria. Beckwith's (1914, p. 217) centrifuge experiments have shown that the 

 plane cuts the mass of mitochondria at any angle, sometimes into very unequal 

 parts, which is in full accord with Lillie's (1908, p. 907) previous work, showing 

 that in the egg polarity is dependent upon the organization of the ground substance 

 itself, not upon the arrangement of any visible granulations within it. 



Before closing this subject it may be emphasized that, so far as I know, there 

 is no valid reason for the general assumption that all forms of polarity, the polarity 

 of secreting cells, the polarity of nerve and egg cell, etc., are referable to the same 

 fundamental cause, which some are inclined to do. An axial gradient in metabolism 

 and the distribution of mitochondria may be factors in one type (i. e., in gland- 

 cells) without having anything at all to do with the others. I am inclined to think, 

 however, that the truly remarkable distribution of mitochondria in secreting cells 

 is much more likely to be one of the results or manifestations of the polarity rather 

 than the cause of it. It may be entirely a question of mechanics, the mitochondria 

 being absent from the distal zone, owing to the pressure of secretion therein. 



