No. 636] GUINEA PIGS AND TUBERCULOSIS 29 



The guinea pigs in lots 10-14 were divided into two 

 groups, those containing at least 25 per cent, of the blood 

 of family 35 and the remainder. Each of these groups 

 was classified by birth rank with results given in Table II. 



TABLE II 



These figures suggest an increase in resistance of the 

 young born in litters up to the third and a decline in re- 

 sistance in young born of aged dams. They must be con- 

 firmed by larger numbers, however, before much signifi- 

 cance can be attached to them. 



The Relation of Age, Weight and Rate of Gain to 

 Resistance 



Mere bulk must be considered as likely to be a factor 

 in resistance to tuberculosis. Other things being equal, 

 one would expect to find that the same inoculation given 

 to a St. Bernard and to a toy spaniel would have a more 

 disastrous effect on the latter. In lots 10-14, some of 

 the guinea pigs were over three times as heavy as others 

 at the time of inoculation (variations hoUveim 120 and 

 440 grams). 



The rate of -aiii is a ,uo..(l indication ..f tlir condition 

 of the animals and is tluis anotluT factor wiiich one would 

 expect to lind cnavlalrd with resistance to disease. In 



weight at days and the rate of -ain between :!:; days 



