MITOCHONDRIA IN TISSUE CULTURES 371 



The only certain method to determine just how and when the 

 mitochondria increase is to follow several living cells through 

 complete cycles. Unfortunately, the cells of tissue culture often 

 round up during late metaphase and anaphase (fig. 15 e, f) so 

 that it is impossible, except in a few cases, to follow the indi- 

 vidual mitochondrium throughout cell division. 



The process of mitosis is an exceedingly slow one compared 

 with that described in other tissues: Prophase 10 to 20 minutes, 

 metaphase and anaphase, 1 to 2 hours; while the period from 

 anaphase including telophase to the daughter cells is an exceed- 

 ingly short one, never more than five minutes from the time the 

 chromosomes are arranged at the opposite poles of the spindle 

 until the cytoplasm is divided, exoept for slender processes, and 

 such stages are correspondingly few in number in the permanent 

 preparations. 



We have not been able to follow the number of mitochondria 

 through a complete cycle of the cell in the living cultures. We 

 have, however, been able to watch the behavior of the mito- 

 chondria during mitosis in a few living cells. Usually the mito- 

 chondria are scattered throughout the cytoplasm and remain so 

 during cell division. About one-half of the mitochondria pass 

 to each daughter cell, namely, those which happen to be on one 

 side or the other of the cleavage plane. In two or three cells 

 during late anaphase most of the mitochondria became arranged 

 in rather of a broad zone around the spindle in the area through 

 which the division plane later formed and one-half of the number 

 of mitochondria passed into each daughter cell. There was no 

 indication of any division of the mitochondrial granules; in fact, 

 in one cell it was clearly observed that several thread-shaped 

 mitochondria passed over entire into one of the daughter cells. 

 A division of the mitochondria such as observed by Meves ('08) 

 and Duesberg ('10) was never observed. We find as did Buch- 

 ner ('09, '10, '11) that this characteristic arrangement of the 

 mitochondria during division of the cell is by no means a con- 

 stant occurrence. 



We have already stated that we are uncertain whether there 

 is an actual or only an apparent increase in the amount of 



