137 



when living cells are immersed in D.O (2). Thus the activities 

 of different intracellular comjxjunds, and hence the relative 

 velocities of various reactions, may be altered when cells are 

 exposed to D>0. Since disturbance of the normal relative rates 

 of physiological processes may cause serious injury to plants 

 and animals, it seems possible that D2O influences life processes 

 by altering the established rate relations of mutually depend- 

 ent intracellular reactions. Other chemical studies have shown 

 that the ratio of the dissociated to the undissociated forms of 

 several compounds changes when D2O is substituted for H2O as 

 the solvent (16, 31). The ratio of dissociated to undissociated 

 molecules in protoplasm might, therefore, be quite different in 

 the two liquids. This kind of disturbance might seriously alter 

 the relative rates of essential reactions in living cells and account 

 for the observed effect of D2O on living organisms. 



D as an mdicator in metabolism. — Although the initial and 

 end products of many physiological processes are known, the 

 intermediate steps by which one is converted into the other are, 

 in many instances, unknown. Recent investigations indicate 

 that the metabolic systems of mice and dogs are unable to dis- 

 tinguish some fatty acids hydrogenated with deuterium from 

 those similarly treated with hydrogen. The analytical chemist 

 can, however, detect the slight difference. Thus by feeding these 

 compounds to animals and later analyzing their body fluids it 

 is possible to trace the intermediate steps in different processes 

 and to obtain elusive information about normal metabolism. 

 For example, physiologists found that even when animals were 

 fed a diet insufficient to maintain their weight, the fat in the 

 diet was not available for use directly, but had first to be de- 

 posited in the fat depots (28), and in another experiment it was 

 possible to trace several intermediate steps in the metabolism 

 of the important substance cholesterol in dogs and to obtain 

 information concerning its behavior in man. 

 Department of Botany 

 Columbia University 

 New York City 



Literature Cited* 



1. Barnes, T. C. 1934. Science 79: 370. 



2. Bonhoeffer, K. F., and O. Reitz. 1934. Naturwissenschaften 22: 744. 



•• For a more complete bibliography of the biological effects of D2O see 

 Pratt (1936). 



