30 



BULLETIN 1090, U. S. DEPARTMENT OF AGRICULTURE. 



and management. At the time they were selected for these two tests there was no 

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

 and weight when they were inoculated. From two to four weeks before inoculation 

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

 and two checks, all of approximately the same weight, and placed in the cages which 

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

 accustomed to being together and to the conditions of care, feed, and management 

 which they were to receive after inoculation. 



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

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

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

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

 directly to the different methods by which they were bred. When the progeny 

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

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

 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 from 

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

 autopsy. 



Table 5 shows the relative susceptibility to tuberculosis of normally bred and 

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

 of death than tuberculosis, the most frequent being pneumonia and inflammation 

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

 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 pneumonia 

 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 these 

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

 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 life after inocula- 

 tion with tubercle bacilli. In each of the eight tests the number of days of life after 

 inoculation was greater in the case of guinea pigs that were not inbred. The shortness 

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

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

 days of life after inoculation for each test, it will be noted that the inbred guinea pigs 

 died 12.49 days sooner than the normally bred pigs. 



Table 5. — Relative susceptibility of inbred and normally bred guinea pigs to disease 

 as determined by inoculation with tubercle bacilli. 





Normally bred. 



Inbred. 





Cause of death. 



eg 



S^cB 

 8§o 



°c = 



C3 o ^J 

 ^.S.CO 



co Co 



gS2 



Cause of death. 



Lesions of T. B. pres- 

 ent but not cause 

 of death. 



Average days of life 

 after injection with 

 tubercle bacilli. 



Test 

 No. 





I 



CD 



c 

 o3 "a) 



1° 



5 



o 

 co 



c 



"c3 2 



si 



03 



"3 

 



I 







c 



~cl"c3 



Co >_. 



<a 



« to 







5 

 



9 



1 



2 



3 



99 

 65 

 12 

 21 

 20 

 15 

 8 

 20 



'"'s 



1 

 4 



1 



2 



2 

 2 



137.2 

 43.6 

 77.2 



117.0 

 72.4 



121.3 

 81.8 



128.5 



79 

 51 

 12 

 25 

 21 

 15 

 8 

 22 



..... 



4 



11 



10 

 7 



1 



6 

 1 

 1 

 2 

 1 



116.6 

 42.9 



74.7 



4. 



2 



3 









2 

 1 



108.7 



5 





1 



4S. 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. si 



3 



1.05 



6 

 2.10 



"i6l.47" 



233 

 78.98 



10 

 3.39 



IS 

 6.10 



19 

 6.44 



15 

 5.09 



88.98 



























