6 BULLETIN 70, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTS ON HORSES. 



In the experiments conducted on horses, 17 animals were used, 

 which were purchased on the open market. Most of the animals 

 were aged, but otherwise in fair condition. All the horses were 

 subjected to the agglutination, complement-fixation, and the ophthal- 

 mic mallein tests, prior to the vaccination. All of them proved free 

 from glanders on all the tests. Since the amount of vaccine to be 

 injected for immunizing purposes has not been established, it was 

 deemed advisable to employ varying quantities for the injections, 

 and in order to determine the resistance of the animals against 

 infection during and after the vaccination they were subjected to 

 exposure at different times during the investigation. 



The smallest amount of the suspension used for the vaccination 

 was the quantity recommended by the New York City Board of 

 Health, viz, 1, 3, and 5 c. c. per injection, while the largest amount 

 any of the horses received was 4, 8, and 12 c. c, respectively. Two 

 of the vaccinated horses received an infection on the nasal mucosa 

 with glanders bacilli, taken up on the end of a platinum loop, one 

 week after the last vaccination. Both of these horses promptly 

 developed glanders and one of them, No. 102, died of an acute form 

 of the disease 21 days after the infection. Thus, there appeared to 

 be no resistance, or at least no increased resistance, against artificial 

 infection. 



To establish the resistance of the vaccinated animals against 

 contact infection a corral was built where all the animals, including 

 two artificially infected glanders cases, were kept. They were fed in 

 common feed boxes and were watered from a common trough. Only 

 one hayrack was used for all animals. Simultaneously with this 

 exposure a stable with three stalls was likewise used for exposing 

 the horses. The construction of the stalls in this stable was such 

 that the animal in the center could reach to the feed boxes of either 

 of the horses in the side stalls. The horse placed in the center was 

 a good discharging case of clinical glanders, whereas the horses 

 placed in the side stalls were either two immunized animals or two 

 controls, all of which were given one week's exposure with this 

 infected horse. This was accomplished by changing the horses in 

 the two side stalls every week, and bringing in two others from the 

 corral, so as to make the exposure as uniform as possible in all ani- 

 mals, including the checks. The conditions of exposure were appar- 

 ently severe, yet they did not exceed the exposure which occurs in 

 the stables of large cities where the sanitary conditions are very 

 poor and where poor light and ventilation afford a splendid oppor- 

 tunity for the propagation of the disease. In fact, the exposure in 

 the corral was rather slight, since the sunlight no doubt had a 

 destructive influence on the infection. 



