BUREAU OF ANIMAL INDUSTRY. 113 



phate. Such a method is complicated, and there is always left in 

 the finished product considerable amounts of ammonium sulphate, 

 Avhich is regarded as undesirable. During the past year a new 

 methoil for heating and concentrating hog-cholera clefil)rinated blood 

 antitoxin has been developed. This consists in heating the old de- 

 fibrinated blood after dilution with a strong solution of sodium 

 chlorid. This is, followed by filtration and subsequent precipitation 

 of the serum proteid, including the antitoxin. Tests of products 

 obtained in this way have indicated that the process is practicable. 

 The details of this process will be published later. 



MODES OF SPREAD OF HOG CHOLERA. 



Extensive experiments to gain further knowledge of the modes of 

 dissemination of hog cholera have been carried out along a number 

 of different lines. In this report there are included only those experi- 

 ments which have proceeded to a stage where a statement of results 

 is warranted. 



Repeated experiments have shown that the blood of pigs that have 

 previously been inoculated with the virus of cholera becomes infec- 

 tious for others within 21 hours. The urine and feces contain the 

 infection usually in 48 hours, and the secretions of the eyes and nose 

 become infectious by the third day following infection. Earely, if 

 ever, do pigs show visible symptoms of cholera earlier than four or 

 five days after infection; therefore these experiments show that 

 infected pigs are capable of transmitting disease before they them- 

 selves show any visible symptoms of illness. 



Experiments were carried out to determine whether by mere con- 

 tact infected pigs are capable of transmitting hog cholera at all 

 stages of the disease or whether there are certain periods, early or 

 late, when the disease is not contagious. These experiments were 

 performed by exposing healthy, nonimmune pigs to infected pigs for 

 short periods of time at different dates following infection. It was 

 found that hog cholera was not transmitted by contact during the 

 first 48 hours following infection. Subsequent to that date and up to 

 and including the twenty-first day after infection the disease was con- 

 veyed regularly to the nonimmune pigs. These experiments show 

 that hog cholera is contagious at practicnlly all stages, even includ- 

 ing the stage of incubation. They indicate also that an infected hog 

 is likely to remain a source of clanger until the time of complete 

 recovery. 



It is "very important to farmers, as well as to persons engaged in 

 live-stock sanitary work, to know whether hogs which have recov- 

 ered from an attack of hog cholera are likely to be " carriers " of the 

 disease. During the past year four hogs which had recovered from 

 distinct and undoubted attacks of cholera were tested for infectious- 

 ness by placing each one in a pen with healthy, nonimmune hogs, 

 and in each case blood was drawn from the recovered pigs and in- 

 jected into nonimmune pigs. In no case was hog cholera produced 

 in the exposed animals, which were later proved to be susceptible to 

 cholera. These experiments do not show that recovered pigs may 

 not at times be carriers of hog cholera, but they do prove that all 

 recovered pigs are not carriers, and they indicate that the likelihood 

 of recovered hogs being carriers of hog cholera is not great. 



33382°— AGE 1917 8 



