1 26 ANXUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



other experiments with nonimmune pigs which were placed in 

 screened pens in which infected house flies were liberated in consid- 

 erable numbers, Avithout the production of a single case of infection, 

 leave a very grave doubt as to whether under natural conditions the 

 house fly is concerned in the dissemination of hog cholera. Likewise 

 it was demonstrated that it is possible for the stable fly to convey 

 infection, either by feeding upon the ears of infected pigs and then 

 biting nonimmune pigs, or by becoming gorged with the blood of 

 sick pigs and then being killed and placed in the feeding trough of 

 nonimmune pigs; but it yet remains to be determined whether this 

 insect is a factor of practical importance in the spread of the disease. 

 Attempts were made to transmit hog cholera by means of mos- 

 quitoes, but the experiments were unsuccessful. A summary of a 

 large part of these investigations was published in the Twenty-Sec- 

 ond Annual Report of the United States Live Stock Sanitary Asso- 

 ciation, page 1^. 



In continuation of work reported last year, four experiments were 

 made under farm conditions in the vicinity of Ames, Iowa, to deter- 

 mine how long the virus of hog cholera persists in pens after the 

 removal of sick pigs. On four farms where hog cholera existed all 

 hogs were removed and susceptible pigs were placed in the vacated 

 lots after intervals of 24 hours, 48 hours, 7 days, and 10 days, re- 

 spectively. In the fii^t case, 1 of the 6 susceptible pigs sickened on 

 the eighth day following exposure and communicated the disease 

 to the others. In the 48-hour and 10-day experiments all the sus- 

 ceptible pigs remained well. In the 7-day experiment 1 sickened 

 and died, though it could not be determined definitely whether it 

 had contracted cholera, while the other 5 remained well. These 

 experiments are merely the beginning of a line of work which seems 

 to be of practical importance and which it is planned to continue as 

 opportunity is found. 



CAUSE OF HOG CHOl.EKA AND RELATED DISEASES. 



In the fall of 1918 investigations of diseases related to hog cholera 

 and resembling it were begun. An infection of this character ap- 

 peared on a farm near Ames, Iowa, among shoats which had pre- 

 viously been given the simultaneous inoculation against hog cholera. 

 The animals presented many of the symptoms commonly seen in 

 cases of hog cholera, but investigation proved that it was a different 

 disease, as hogs which were firmly immune against hog cholera con- 

 tracted the other disease when exposed in the infected lots. The 

 main characteristics of the disease were an inflammation of the large 

 intestines, which showed on dissection a superficial layer of necrosis 

 on the mucous surface, while beneath this there was a zone in which 

 hemorrhage was more or less marked. The condition thus observed 

 was no doubt what has been commonly termed necrotic enteritis. 

 Microscopic examination revealed in the zone beneath the necrotic 

 area typical threads of Bacillus necrophorus. Rabbits inoculated 

 Avith bits of the diseased intestine developed typical necrophorus in- 

 fection. The disease seems to be increasing in prevalence in certain 

 of the Western States, and further efforts are being made to dis- 

 cover its cause and means of prevention. 



