30 



W. M. Dale 



In Table I is listed the protective power of various sulphur- 

 containing compounds, when radiation took place with carb- 

 oxypeptidase as the indicator. Qp is the protective power 

 per iig. of protective substance, and Qg is the protective power 

 of such amounts of protector as contain one [ig. of sulphur in 

 each case. One can, therefore, estimate how the non-sulphur 

 residue in any one compound affects the protective power of 

 one [jLg. of sulphur contained in it, taking the colloidal sulphur 

 as reference. Elemental sulphur is about as protective as 

 thiourea and sodium thiosulphate, but the introduction of 



Table I 



The Protective Power of Various Sulphur- 

 containing Compounds with Carboxypepti- 

 dase as the indicator 



Thiourea 

 Dimethylthiourea 

 Colloidal sulphur 

 Sodium thiosulphate 



two methyl groups into thiourea causes a considerable de- 

 crease in the protective power of the sulphur. 



Because of its possible bearing on cell constituents, I should 

 not omit to mention that the straightforward sharing mechan- 

 ism of radicals between two solutes is not always valid. If it 

 were, the protective power per unit weight of protector would 

 be constant, whereas in certain cases it declines appreciably 

 with increasing concentration of protector. This declining 

 protective power may be of significance from the biological 

 point of view when the effect of protective substances within 

 the interior of cells is considered. The phenomenon, which we 

 called the "changing quotient", is shown in Fig. 3, in which 

 the log of the protective power Q is plotted on the ordinate, 

 and the concentration of the protector on the abcissa. In 

 these experiments carboxypeptidase was used as the indicator. 



