No. 631] CONGENITAL PALSY IN GUINEA-PIGS 141 



ants of two homozygous normal individuals, even though 

 their feeding and care is in all respects similar to that of 

 the others. In other words, the disease has behaved 

 strictly in accord with the known principles of heredity 

 since it has been under observation, and we have every 

 reason to believe that it has not appeared spontaneously 

 during that time. This would mean then that if the dis- 

 ease was due to nutritive conditions, it must have had its 

 inception in the stock before we received it, or within a 

 very short time thereafter at latest. 



The evidence that heritable defects of this sort may be 

 induced by external conditions is very meager at best, 

 Stockard has produced somewhat similar nervous de- 

 fects in guinea-pigs by the administration of alcohol, but 

 while he claims that these are heritable, he has not, so far 

 as we are aware, shown that any of them are inherited in 

 strict Mendelian fashion as is the defect with which we 

 are concerned. We are therefore led to believe that this 

 character in our stock has not been induced by nutritional 

 or other environmental causes, but that it is due to a 

 factor mutation similar to those which have been studied 

 so thoroughly in domesticated and experimental animals 

 and plants in recent years, and for which there is at pres- 

 ent no assignable cause. 



2. It might perhaps be assumed that the palsied indi- 

 viduals are due to unfavorable uterine conditions and con- 

 sequent abnormal foetal development. The occurrence of 

 "rtmts" in swine and in other animals which produce 

 large litters show that the uterine conditions are not the 

 same for all the individuals in a litter. Some doubtless 

 have a poorer maternal blood supply than others, or they 

 may be crowded, or twisted into a position unfavorable 

 for growth. That these are not factors in the present 

 case seems demonstrated, however, by the fact that the 

 palsied animals are on the average fully as large and well 

 developed at birth as their litter mates (see Table IV). 



3. The necessity of inbreeding the original stock in 

 order that the recessive palsy condition should appear is 

 apparent ; but it might be maintained that this inbreeding 



