No. 636] GUINEA PIGS AND TUBERCULOSIS 49 



ing 1919 requires some consideration. The general con- 

 dition of the stock was much better in 1919 than in any 

 of the three preceding years. The principal cause of the 

 high death rate, small and infrequent litters and slow 

 growth during 1916, 1917 and 1918, especially during the 

 first half of each year, was probably an insufficient sup- 

 ply of green feed during late winter and early spring. 

 Symptoms, such as lameness, swollen and bleeding gums, 

 were noted rather frequently. These were probably in- 

 dicative of scurvy. A form of pneumonia was also rather 

 common. Whether tuberculosis was present in the stock 

 at this time is not certainly known. It is doubtful, as 

 guinea pigs seldom take the disease unless directly inocu- 

 lated. However, this may be, it seems probable that 

 family 35 has a special ability to withstand exceptionally 

 adverse conditions. It is not unlikely that this character- 

 istic may be connected directly or indirectly with its re- 

 sistance to tuberculosis. Under good conditions, on the 

 other hand, there seems to be little if any relation between 

 this form of vigor and apparent vigor in other respects. 



CoXCLUSIOJsS 



There is little or no relation among guinea pigs be- 

 tween resistance to tuberculosis and sex. The present 

 data indicate a possible superiority of the males, but one 

 which is too slight to be certainly significant. 



The data suggest a slightly greater susceptibility among 

 the progeny of very young or ver\' old females but this 

 also is of doubtful significance. 



Size of litter, birthweight and rate of gain up to wean- 

 ing give virtually no indication of the probable length of 

 life after inoculation. 



The rate of gain preceding inoculation and the age 

 and weight at that time all together determined less than 

 7 per cent, of the variation in length of life in a very 

 heterogeneous lot of guinea pigs and less than 2 per cent, 

 in a somewhat more homogeneous lot. 



Marked differences in resistance were found among a 

 number of inbred families of guinea pigs. 



