114 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



The belief that birds play an important part in the spread of hog 

 cholera led to some experiments with pigeons. Suitable pens were 

 prepared facing each other, and the space between was inclosed by 

 wire netting. The front of each pen was left open, so that pigeons 

 which were placed in the inclosed space between the pens could have 

 easy access to the pens on either side. In one pen pigs sick of cholera 

 were kept and in the other there were healthy, nonimmune pigs. 

 When the sick pigs died they were replaced with others, so that the 

 disease was kept constantly present in one of the pens, and this pen 

 was not cleaned during the course of the experiment. The healthy 

 pigs were changed from time to time. The pigeons constantly flew 

 from the infected pen to the opposite pen containing the well pigs, 

 which was only 10 feet distant. In the different experiments healthy 

 pigs were exposed to infection through the medium of the pigeons 

 for from 30 to 40 days. In no case was the disease transmitted by 

 the pigeons, although it is evident that every opportunity was 

 afforded for this to occur. The exposed pigs were proved susceptible 

 by subsequent exposure to cholera. While these experiments can not 

 be said to prove that it is impossible for pigeons to carry hog cholera, 

 it seems fair to conclude that the disease is probably not often carried 

 from one farm to another in that w^ay. 



Eats were fed for a number of days on meat from pigs that had 

 died of hog cholera, and later the rats were killed and fed to sus- 

 ceptible pigs, but in no case was cholera conveyed in this way. 



A number of experiments were carried out to determine the length 

 of time that premises are likely to remain infectious following an 

 outbreak of cholera. The attempt was made to simulate as far as 

 possible ordinary farm conditions. Pens of different construction 

 were used, some having dirt floors, others concrete floors, and others 

 wooden floors. All of the pens were so constructed or so situated as 

 to be almost wholly protected from sunlight. Sick pigs were placed 

 in these various pens ; in some the pigs were allowed to die before the 

 pen was used for purposes of exposure; in others the pigs were 

 removed during the height of the disease after they had been plainly 

 sick of cholera for a number of days. Susceptible pigs were placed 

 in these different pens at different periods of time after the removal 

 of the sick pigs. The first experiments were carried out during the 

 summer and fall, whereas the second set was carried out in December 

 after the weather had become cold. The results may be briefly sum- 

 marized as follows: 



In the warm weather of the late summer and early fall healthy 

 pigs did not contract cholera when placed in pens 24 hours after they 

 had been occupied by pigs sick of cholera. In the colder weather of 

 the late fall and early winter the pens remained infectious for much 

 longer periods. There was no apparent difference in the duration of 

 infection in the various types of pens. The results of these experi- 

 ments are surprising, as the general opinion of those who have 

 studied hog cholera has been that the virus survives for many 

 months. As these experiments are considered of great importance, 

 they are being continued and repeated. 



In another series of experiments carcasses of hogs that had died 

 of cholera were exposed in the open in a metal wheelbarrow, where 

 they were protected from the direct sunlight, while others were 

 buried at a depth of 2 feet from the surface of the ground. Portions 



