No. 636] GUINEA PIGS AND TUBERCULOSIS 



45 



whether these dififerences in resistance are related to any 

 of the other characteristics in which these families differ. 



We may dismiss color with a few words. Families 32 

 and 39 produce only animals of the primitive golden 

 agouti color; families 2 and 13 produce only blacks, a 

 color which differs from golden agouti by a single re- 

 cessive factor ; family 35 is composed of yellow agoutis. 

 This color is recessive to golden agouti, depending on an 

 allelomorph of albinism. We can not attribute the high 

 resistance of family 35 to the yellow agouti color since 

 the even more highly resistant crossbreds between family 

 35 and the other families are all of the golden agouti 

 color also found in the susceptible families 32 and 39. 



In all of the families there are varying amounts of 

 white in a piebald pattern. and of red or yellow in a tor- 

 toise-shell pattern. No influence can be attributed to the 

 amount of w^hite unless it is assumed that an inter- 

 mediate condition is superior to either extreme. Family 

 39 has the least white, averaging less than 20 per cent. ; 

 families ] 3 and 32 have the most, averaging over 80 per 

 cent.; while families 2 and 35 are intermediate with 

 about 70 per cent, and 60 per cent, white, respectively. 

 It may be added that the correlation between the amount 

 of white in the coat and length of life in family 35, lots 

 10-14, was found to be virtually zero. Similarly, family 

 35 is intermediate between family 39 with least red and 

 family 2 with most red in the colored parts of the coat. 



The records in size, fertility and death rate among the 

 inbred families and cross breeding experiments during 

 the year 1919, in which all of these tested animals were 

 born, is given in Table XVI. In this table, the weights 

 and mortality records are corrected for the important 

 effects of size of litter by calculating separately the aver- 

 ages in litters of 1, 2, 3 and 4 and finding an index in 

 which these averages are weighted 1, 3, 3 and 1, respect- 

 ively. This means practically that all of the records 

 are reduced to the basis of an average size of litter of 2.50. 



Because of the method of averaging, the figures are 



