ON THE DOMESTIC FOWL. 257 



deleterious agent, and which we may designate as class (a), we may 

 fairly assume that there is a possibility of two other classes existing, 

 viz., (b) germ cells which, while not completely inactivated, are so 

 injured by the agent as to produce zygotes which are measurably 

 defective in some degree, and (c) germ cells which are not measur- 

 ably affected by the agent at all in the dosage employed, and produce 

 zygotes which are not discernibly otherwise than perfectly normal. 



4. It appears entirely fair to assume that germ cells of the 

 (a) class are of relatively the lowest mean vigor or resisting power, 

 class (b) next, and class (c) the highest. The proportionate num- 

 ber of the two sorts of zygotes corresponding to classes (b) and 

 (c) of germ cells which would be expected to appear in any experi- 

 ments made to test the point would clearly be a function of the 

 mutual relationship or proportionality between two variables, the 

 dosage of the deleterious agent on the one hand, and the mean 

 absolute resisting power of the germ cells characteristic of the strain 

 or species of animal used in the experiments on the other hand. 



5. If the dosage of the agent be relatively high in proportion to 

 the mean absolute resisting power it would be expected that all the 

 germ cells would fall into classes (a) and (b), producing no zygotes 

 at all or zygotes in some degree defective. This about represents 

 the condition, so far as can be judged from the data given, with 

 Stockard's alcoholized guinea pigs and Weller's*^ lead-poisoned 

 guinea pigs. The dosage is sufficiently high in proportion to the 

 absolute germinal resisting power that all or practically all of the 

 offspring are defective in greater or less degree and in reference to 

 some one or more characters. Stockard's Fo and F3 results indicate 

 that though the untreatd F^ animals from alcoholists may appear 

 normal, they really are somewhat defective. 



6. If, on the other hand, the dosage, though absolutely the same, 



be relatively lower in proportion to the mean absolute resisting 



power of the germ cells it would be expected that all three germ 



cell classes (a), (b) and (c) would be represented. The zygotes 



actually formed would be chiefly produced by (c) germ cells, and 



to a much smaller extent by (b) cells. Under these circumstances 



it would necessarily follow that a random sample of the zygotes 



6 Weller, C. V., " The Blastophthoric Effect of Chronic Lead Poisoning," 

 Jour. Med. Research, N. S., Vol. XXVIIL, pp. 271-293, 1915. 



