174 Harry Lewis Wieman. 



expect to result from a reduced oxygen supply. A very rapid in- 

 crease in cell multiplication would cause a temporary diminution 

 in the oxygen supply for each individual cell. The stimulus to 

 increased cell division is a distinct factor that is bound up in the 

 process of building cysts of the testis. As soon as the sudden in- 

 crease in number of cell has been compensated by a corresponding 

 increase in oxygen supply, the conditons required for mitosis are 

 restored. 



Child's observations upon the cestode Moniezia offer further 

 suggestions along this line. This form is not only relatively low in 

 the animal scale, but one which, inadditionhas undergone degener- 

 ation : a combination of circumstances which would lead one to 

 expect primitive methods in cell division as well as in general 

 metabolic processes. Here amitosis appears to be the regular 

 method of cell division, while mitosis is comparatively rare, occur- 

 ring only during the maturation period and early cleavage stages. 



What causes the change from mitosis to amitosis? It has appear- 

 ed to me that here likewise a gradual diminution in nutrition is 

 responsible. It might be assumed that the object of the long rest 

 stage or growth period in the development of the ovum is to elab- 

 orate food and formative materials for maturation, fertiliza- 

 tion and embryonic development. We might further assume that 

 the same process provides for a certain number of mitotic divi- 

 sions extending through the early cleavage. The direct method of 

 cell division sets in because of a deficiency in the amount of nutri- 

 tive material (oxygen?) necessary for continued mitotic divisions. 

 This is in keeping with the fact that amitosis occurs usually under 

 abnormal metabolic conditions which are unfavorable to normal 

 metabolic processes. Amitosis might be regarded as a simpler 

 form_ of cell division, not so much because it takes place in the 

 absence of spindle and chromosomes, as for the reason that it 

 can occur under circumstances that make mitosis impossible. 



In accordance with this idea one notices that amitosis has been 

 observed most frequently under conditions of rapid growth, 

 where if this explanation is applied ,the cell makes use of the direct 

 method of division rather than follow the slower and more com- 

 plex mitotic method largely because of limitations in the way of 



