378 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



00" C. for 30 niimites the blood taken from sick pigs. As the attenua- 

 tion of the hog-cholera virus, if this could be carried out with regu- 

 larity and with certainty, was a matter of much interest and impor- 

 tance, experiments were carried out to determine the correctness of 

 this work. In these experiments two lots of virus were used. The 

 blood was heated for 30 minutes at 00° C. In one case phenol was 

 added to nil of the virus immediately after heatin*^ and cooling. In 

 the other lot, half of the heated virus was phenolized, while to the 

 other half no addition whatever w^as made. The phenol was added 

 in amount sufficient to secure a concentration of one-half to 1 per cent. 

 It does not seem necessary at this time to go into the details of these 

 experiments, but the Avork may be summarized as follows: Fourteen 

 nonimmune pigs were inoculated with the heated virus. All of these 

 contracted hog cholera from the injection, and 12 died of the disease. 

 It is our opinion from these experiments and from others previ- 

 ously carried out that the employment of hog-cholera virus supposed 

 to be attenuated by heat is dangerous, because such inoculations may 

 set up disease in localities where it has not previously existed. If, 

 however, the virus has been heated to such an extent that it does not 

 produce disease, it is more than likely it will not give the desired 

 protection from hog cholera. 



PRACTICAL WORK IN COMBATING HOG CHOLERA. 



During the past year there has been greatly increased interest on 

 the part of officials in the various States and of farmers and stock 

 raisers generally in the work of combating hog cholera through the 

 use of the serum developed by this bureau. At the present time 30 

 of the States are engaged in distributing serum. In a few States, 

 wdiere the amount of money available is small or where the hog in- 

 dustry is not largely developed, the States have purchased serum 

 of private manufacturers and distributed it to farmers in the State 

 at cost. By purchasing in this way on a large scale the States are 

 able to make the serum available to farmers at a lower price than it 

 could be purchased for in small amounts. The vast majority of the 

 States which are engaged in this work, however, have established 

 laboratories ancl are manufacturing serum in greater or less amount 

 for distribution to farmers. In some States the serum is supplied 

 free of cost. In others the States charge the cost price of manufac- 

 ture. There is little uniformity in this practice or in the method 

 of applying the serum. There are States which permit the serum 

 manufactured by them to be applied only by State officials. Others 

 require the employment of a licensed veterinarian, and still others 

 supply to farmers direct upon application. In no State has the work 

 progressed to such a point that a systematic attempt to eradicate 

 the 'disease has been practicable. As this is without doubt the ulti- 

 mate object sought by all officials, we may expect that the next few 

 years will see the inauguration of a determined effort to eradicate 

 this disease in at least some of the large hog-raising States. 



Precisely accurate statistics regarding the amount of serum which 

 has up to the present time been manufactured and distributed by 

 State authorities have been difficult to obtain. Through a series of 

 inquiries, however, in which the various State authorities have kindly 

 cooperated by furnishing data at their disposal, it appears that con- 



