30 



EULLETi:^" 1090, TJ. S. DEPAETMEXT OF AGPJCrTLTURE. 



and management. At the time they were selected for these two tests there was e 

 apparent difference in principals and checks. All were practically the same ag 

 and weight when they were inoculated. From two to four weeks Tjefore inoculatio 

 the animals which were to be inoculated were selected in groups of four, two principa. 

 and two checks, all of approximately the same weight, and placed in the cagea whic 

 they were to occupy after inoculation. This was done so that they could becom 

 accustomed to being together and to the conditions of care, feed, and ma,nagemer 

 which they were to receive after inoculation. 



The guinea pigs which were used in the remaining six tests here reported wer 

 the progeny of selected stock, both the seventh generation inbred and the normall 

 bred individuals. They were kept under exactly the same conditions from the ttm 

 they were born until they died, so that results obtained from them may be attribute^ 

 directly to the different methocfs by which they were bred. When the progen; 

 of this selected stock were large enough — which was when they weighed betwee: 

 400 and 500 grams — they were selected according to size and age and placed in peni 

 as indicated in the case of the first two tests, preparatory to inoculation. After inocula^ 

 tion with tubercle bacilli they were kept in the same cages until they died fror 

 tuberculosis, or for some other cause which was determined so far as possible b; 

 autopsy. 



Table 5 shows the relative susceptibility to tuberculosis of normally bred an( 

 seventh-generation inbred guinea pigs. It will be seen that there were other cause 

 of death than tuberculosis, the most frequent being pneumonia and inflammatio] 

 of the bowels. A greater percentage of normally bred than inbred guinea pigs die< 

 of generalized tuberculosis. This is accounted for by the fact that a larger percentage 

 of the inbred stock died of other diseases after inoculation, principally pneumonit 

 and inflammation of the bowels. It is probable that their vitality had become di 

 minished to such an extent through inbreeding that they easily succumbed to thesi 

 diseases. In both tests there were instances where the lesions of tuberculosis wen 

 found on autopsy, but death was due to some other cause. The comparative resist 

 ance to tuberculosis will be apparent on noting the number of days of Hfe after inocula 

 tion with tubercle bacilU. In each of the eight tests the number of days of life afte: 

 inocidation was greater in the case of guinea pigs that were not inbred. The shortnesi; 

 of the time which the animals in some of the tests lived after inoculation was due tc 

 the extreme -virulence of the organism used. Considering the average number o 

 days of hie after inoculation for each test, it will be noted that the inbred guinea pig! 

 died 12.49 days sooner than the normally bred pigs. 



Table 5.- 



-Relative susceptihility of inbred and normally bred gvAnea pigs to disease 

 as determined by inoculation with tubercle bacilli. 





Xormally bred. 



Inbred. 





Cause of death. 



c S o 



Z.'$.j. 



Or- — 



■=.£.0 

 o^c; — 



Cause of death. 



Lesions of T.B. pres- 

 ent but not eaiiso 

 of death. 



AvoraRG days of life 

 after injection with 

 tubercle bacilli. 



Test 

 No. 



._, o 

 SI 



S 



S 



5 

 C 



II 



5 o 



§ 

 o 



£.2 



— O 



£l 



23 



0^ 



.3 



•s 



S 

 s 



^ 



~ c 



■3 



1 



2 



3 



99 

 65 

 12 

 21 

 20 

 15 

 8 

 20 



5 



1 

 4 



1 

 2 



2 

 2 



137.2 

 43.6 

 77.2 



117.0 

 72.4 



121.3 

 81.8 



12S.5 



79 

 51 

 12 

 25 

 21 

 15 

 8 

 22 



6" 



4 

 11 



10 

 7 



1 



6 



} 



2 



1 



116.6 

 42.9 



74.7 



4. 



2 



3 











2 



1 



108.7 



5 





1 



4.8.2 



6 







104.7 



7 











1 

 3 









68.8 



8 



1 







1 





1 



4 



117.2 











Total 

 P.ct. 

 Av... 



260 

 91.23 



8 

 2.81 



8 

 2.81 



3 

 1.05 



6 

 2.10 



'i6i.'47' 



233 



78.98 



10 

 3.39 



18 

 6.10 



19 



6.44 



15 

 5.09 



88. 98 



























