394 MARGARET R. LEWIS AND WARREN H. LEWIS 



intimately connected with all transformations of the cytoplasm. 

 On the other hand, we must bear in mind the fact that many 

 observers have neglected to identify the body which they had 

 under observation in such a manner that one can be certain 

 that they had the same body which another observer would 

 term mitochondria. It is quite doubtful whether all the bodies 

 called mitochondria are really the same. 



The criterion for mitochondria in the embryonic cell, as stated 

 by Duesberg after Montgomery, is one which the observer would 

 hesitate to carry out, but some criterion in the sex cell, in the 

 embryonic cells and also in the adult cells should be established 

 for the mitochondria, which all workers will endeavor to fulfil, 

 in order that there may be some common ground for discussion 

 of the results obtained by the numerous observers at work in 

 this field. 



CONCLUSION 



1. Tissue cultures afford an excellent method for observations 

 upon an undisturbed cell as it lives, divides and grows in a 

 medium of known chemical constitution; for experimental work 

 on a living cell; and for the study of the process of fixation. 



2. These living cells do not correspond to the usual concep- 

 tion of a cell obtained from the study of fixed material. Both 

 cytoplasm and nucleus are finely granular, almost homogenous 

 in appearance. There is no sign of a reticular or of an alveolar 

 structure of either the cytoplasm or nucleus. Osmic acid 

 vapor is the best fixative for these cells. 



3. Mitochondria are present in all the cells of these growths 

 as slightly refractive, large or small granules, rods and threads, 

 similar to those of the chick embryo cell. The mitochondria 

 can be followed and studied in the living unstained cell for 

 hours. 



4. The mitochondria may be scattered throughout the cyto- 

 plasm or they may be located around the nucleus or around 

 the idiozome. Any one mitochondrium may change its position 

 in regard to other mitochondria or in regard to the entire cell. 

 Mitochondria located around the centra^some may later migrate 



