PROTECTION FROM TOXIC REAGENTS 215 



then the survival depends on the volume of the medium for any giv- 

 en concentration of the toxic agent and also upon the density of the 

 population. The same relationship holds if the active lethal agent 

 works through capillary attraction or by division among phase 

 boundaries. These relationships are recognized as forming a bio- 

 logical aspect of the law of mass action. 



In experiments on the brine shrimp, Artemia salina, exposed to 

 reduced or to increased salt solution, Pawlow found that the theory 

 given above was verified. The mean life-duration varied from 32.1 to 

 6.1 in different salt concentrations when the volume was quad- 

 rupled, while halving the numbers of animals present decreased the 

 survival between 6.7 and 15.2 per cent. Similar relationships were 

 found for the amphipod Gammarus pulex when exposed to certain 

 concentrations of NaCl. 



Stimulated to similar studies by their interest in the implications 

 of the work of Gurwitsch on mitogenetic rays, Frank and Kurepina 

 (1930) have demonstrated mass protection for sea-urchin eggs from 

 the action of KCN, both as regards the rate of development and the 

 percentage surviving. They report that io~^ N solution exerted the 

 following effects: 



Number of eggs i in each 13 drops 68 in 3 drops 



No cleavage 85 % 20% 



2 blastomeres 15% 4°% 



4-8 blastomeres 0% 40% 



Another type of protection has already been shown to be operat- 

 ing, in at least certain instances, with aquatic forms (chap, vii) and 

 is of sufficient importance to be repeated here in some slight detail. 

 The discovery of this factor is a result of the work of Fowler (1931), 

 who has examined the resistance of Daphnia pulex to a great many 

 chemicals. Usually he found the groups more resistant than were 

 isolated individuals run in the same volume of the same solutions. 

 When he pushed the analysis of this phenomenon, particularly with 

 CaCL, he found that the group was consuming less oxygen per in- 

 dividual for a given exposure time than were the accompanying 

 single individuals. Further, when the experiments were run in such 

 a way that the CO2 was absorbed as soon as produced, the survival 



