ENERGY SUPPLY AND MITOTIC DIVISION 191 



cdncluded that within wide limits the number of resting cells which 

 enter prophase is in direct proportion to the sugar concentration, whereas 

 for the completion of these divisions sugar is much less important. 



The importance of carbohydrate metabolism for desoxyribonucleic 

 acid formation follows also from the observation of Roberts (6). The 

 incorporation of P^^ into desoxyribonucleic acid in E. coli is very mark- 

 edly reduced (by a factor of 7) when the cells are partially depleted of 

 potassium. Potassium is involved in the glucose cycle, and interference 

 with the cycle is presumably responsible for the reduction in the rate of 

 desoxyribonucleic acid formation. 



The use of narcotics, such as nembutal, which among other effects 

 reduces oxygen consumption, was found to partially inhibit the incorpo- 

 ration of P^^ into the Jensen sarcoma of the rat (17). 



In this connection, the investigation of Medawar (7) should be men- 

 tioned as well. Working with epidermis in vitro, he found that an in- 

 crease in oxygen concentration resulted in increased mitotic activity, 

 and conversely that strictly anaerobic conditions prevented all mitosis, 

 although the cells might survive for a week. 



Oxygen and enzymes involved in sugar metabolism are, therefore, re- 

 quired for supplying the energy used in the mitotic process, especially 

 at the onset. The doubling of the nucleic acid and other cellular con- 

 stituents must involve considerable amounts of work, in which a signifi- 

 cant quantity of sugar and oxygen may be involved. 



Runnstrom (8) and Brachet (9), working with sea-urchin eggs and 

 amphibian eggs, respectively, found a peak in oxidation during prophase. 

 Zeuthen (13), however, working on a number of different eggs such as 

 those of the frog and sea urchin found in all cases a slight continuous 

 rise in respiration beginning during the first part of mitosis, followed 

 by a subsequent decrease. The respiratory peak was around metaphase 

 or anaphase. Thus, respiration proceeded at an increasing speed during 

 the period of synthetic activity. 



In developing anthers, Erickson (10) observed a pronounced fall in 

 oxygen consumption during the transition from the interphase to the 

 prophase. Other evidence (11) has been presented of a drop in respira- 

 tion during this transition. Furthermore, Zeuthen (12, 13, 14) found, 

 in the interval of the development of egg cells in which interphase is 

 practically absent, that the respiration rate remained almost constant. 

 After approximately six divisions had taken place the mitotic rate slowed 

 down, presumably because, at least partly, of the appearance of inter- 

 phases. By this time, when interphases became visible, respiration in- 

 creased markedly in a stepwise manner, each step coinciding with a 

 mitotic cycle. How far interphase and how far prophase is responsible 



