8 BULLETIN 1090, U. S. DEPARTMENT OF AGRICULTURE. 



Table 2. — The relative homogeneity of the inbred families. 



[The number of matings made in each family from 1906 to 1909 (first line of each family) and from 1910 

 to 1915 (second line of each family) is given in the second column. The maximum percentage of these 

 matings descended from a single mating in each generation is shown in the following columns. Change 

 in the dominant subfamily is indicated by an asterisk.*] 



Fam- 



No. 



Generation. 



Fam- 

 ily- 



No. 



Generation. 



ily- 







1 



2 



3 



4 



5 



6 







1 



2 



3 



4 



5 





7 



8 



1 



11 



13 

 36 

 65 

 41 

 40 

 43 

 77 

 26 

 59 

 73 

 71 

 67 

 94 

 42 

 41 

 23 

 8 

 38 

 88 

 25 

 62 

 19 

 43 



100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



55 

 100* 



50 



71 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



91 

 100 



44 



89 



63 



98 



51 



69 



96 

 100 



75 



72 



54 

 100* 



48 



68 



44 



75* 



63 



66 



96 

 100 



95 

 100 



27 



92 



31 



89 



44 



55 



40 



65 



46 



88 



25 



45 



28* 



80* 











20 

 21 

 23 

 24 

 31 

 32 

 34 

 35 

 36 

 38 

 39 



23 

 48 

 20 

 96 

 12 

 45 

 66 

 63 

 32 

 64 

 103 

 107 

 11 

 34 

 45 

 95 

 47 

 94 

 40 

 61 

 14 

 77 



100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



61 



98 



95 

 100 



83 

 100 



55 



59* 



53 



53* 



62 



40 



91 

 100 



98 

 100 



96 

 100 



43 



92 



93 

 100 



52 

 98 

 50 

 100 

 50 

 96 

 29 

 59* 

 28 

 53* 

 23 



13 

 83 

 35 

 89 

 25 

 49 















92 



85 



62 



31 



52 



42 









2 











86 



74 



57 



34 



48 





1 





3 











33 

 23 



47 

 19 

 76 



















7 



























29* 













9 





















46 







53* 



45* 











11 



































13 











64 



100 

 29 

 59* 

 47 

 60 



19 



44 















46* 



















14 





















41* 











59* 



59* 



59* 



59* 



58 



"V\ 



15 



















::::::: 



41 









1 



17 



42 

 41 

 56 

 76 



88 

 84* 































92 

 86 

 100 



92 



71 

 100 



49 

 64 

 100 











18 



52 

 76 

 32 



84* 



20 

 37 







29 

 56 















56 



31 





19 











49* 





















































From 1906 to 1911 the inbred stock, as already stated, was kept at 

 the bureau Experiment Station at Bethesda, Md., with many other 

 guinea pigs raised for pathological experiments. In 1911 the inbred 

 stock was taken to the experiment farm at Beltsville, Md. Shortly 

 before moving, 40 pairs of normally bred guinea pigs were selected on 

 the basis of vigor and set aside as a control stock to be maintained 

 without inbreeding. They were from the same stock from which 

 Families 1 to 24 and the original females of Families 31 to 39 were 

 derived. They had, however, been maintained up to 1911 without 

 records. This control stock was called Experiment B. It has been 

 kept at Beltsville since 1911 under the same conditions as the inbred 

 families except that matings as close as those between second cousins 

 have been avoided. 



SYSTEM OF MATING, CARE, AND FEED. 



With rare exceptions, the matings in the inbred families have been 

 made between litter mates at the time of weaning at 33 days. This 

 was to avoid mistakes in identity which would make the strictness of 

 the inbreeding doubtful. Females occasionally are sufficiently mature 

 at 33 days to bear litters sired by their own sire at about 100 days of 

 age. They do not appear to suffer ill effects, and as the males do not 

 become mature until over 2 months of age, the system of breeding 

 followed is not believed to be injurious to the animals to an appre- 



