NEUTRON' EFFECTS OX AXIMALS 9 



balance, or milieu interne, represents a dynamic equilibrium in which en- 

 zymes are continuously catalyzing not only degradation and regeneration 

 reactions, but also chemical reactions to make available for synthetic proc- 

 esses the energy acquired from the environment. The vital balance is 

 determined, not only by the thermo-dynamic potentials, but also ])y the 

 kinetics of the individual reactions catalyzed by the enzymes. 



A^ery minute particles often play an extraordinarily large part in the 

 metabolism of living tissue. For exam.ple, the growth hormcne from the 

 pituitary recently discovered by Evans of California is so powerful that ten 

 gammas, ten-millionth of a gram, is sufficient to bring about a gain of 

 weight of one gram a day in rats whose pituitary gland has been removed. 

 This is only one example of the power which certain substances in very 

 minute amounts have upon growth and reproduction of cells. 



If the popular explanation of the physicists of absorption of quanta is 

 to be made intelligible, it must be considered where, in the cell system, this 

 absorption takes place. To take the homely metaphor of the automobile, 

 if a bullet is fired from a rifle and hits the machine, the force is absorbed; 

 but if it is absorbed on the fender, it does little harm and if it is absorbed 

 on the timer, the machine is dead. How much more complicated and how 

 much less understood is the dynamic cell system. If the quanta are ab- 

 sorbed on Evans' growth hormone, as quite well might be possible, then 

 growth stops as do the white blood cells after neutron bombardment. 

 It may be the destruction of the sensitive entity which prevents the growth 

 and reduplication of cells. The mode of destruction might quite well be in 

 a breakage of the weaker molecular linkages of the molecules concerned as 

 seemis to be the case in the effects from shorter ultraviolet light from 2654 A 

 to 2536 A. 



With the background of our previous work on the treatment of cells by 

 shorter ultraviolet light and the absorption of these wave lengths by the 

 nucleic acid of the cells, it was natural to begin studies in regard to enzymes 

 concerned, particularly desoxyribonuclease, but this enzj'me was shown 

 not to be affected by neutron bombardment. Recent work by Dale, 

 Meredith and Tweedie (4), however, has shown that in certain enzymes 

 there is a protective or indirect action from additional substances in the 

 solution capable of reacting ^^■ith the intermediate products and so diverting 

 some of the radiation to itself. The effect of X-rays on aqueous solutions 

 of enzymes has been frequently interpreted in terms of the "quantum hit" 

 theory without proper consideration of the indirect action. The effect 

 depends upon the concentration and purity of the enzyme solutions and so 

 shows reactions which would not be present in the vital systems owing to 

 protective substances. This complicates the matter. Radiation produces 

 a smaller effect with the added protective substances which are often too 



