246 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



The literature is voluminous and there is a lack of agreement among 

 the various writers with respect to the precise mechanism of col- 

 loidal phenomena. In view of the somewhat unsettled condition in 

 this field, it was decided to abandon the idea of a study of colloidal 

 reactions in general as originally planned, and to concentrate upon 

 intensive study in narrower fields in order to develop the various 

 principles and their particular application one at a time. 



HOG-CHOLERA INVESTIGATIONS. 



In continuation of investigations on hog cholera, much attention 

 has been given to the immunization of suckling pigs by the simul- 

 taneous method. It is evident that if all pigs could be successfully 

 immunized when very young many advantages would accrue. In 

 order to determine whether or not the immunity following the simul- 

 taneous immunization of young pigs is actually of short duration, 

 or whether it may be expected to last as well as when the same treat- 

 ment is given to older pigs, arrangements have been made with the 

 Animal Husbandry Division to immunize all of the young pigs pro- 

 duced at the various experimental farms under the control of that 

 division. Nearly 3,000 pigs have been treated during the suckling 

 period without any loss from treatment and so far without the dis- 

 covery of susceptible pigs among those that were tested from three 

 to six months after treatment. It is too early to, announce final con- 

 clusions. The tests are being continued. 



A study of the causes which are responsible for the so-called breaks 

 in immunity following simultaneous immunization has been con- 

 tinued. Careful experiments repeated and carried out on a large 

 number of hogs have shown that hog-cholera virus of good potency 

 may be expected to produce disease when injected subcutaneously in 

 doses of one three-hundred thousandth of a cubic centimeter. This 

 fact alone seems to indicate that the failure to obtain immunity after 

 simultaneous inoculation in some cases is probably not due to the em- 

 ployment of too small a dose of virus but rather to some defect in 

 the quality of the virus. A few cases have again come to notice 

 where there was a failure to preserve the virus properly, but a sys- 

 tematic examination of the virus produced during the course of reg- 

 ular business by licensed establishments has resulted in the finding 

 of a very satisfactory and uniform virulence. It is quite possible, 

 however, that in practice when hog-cholera virus is sent from the 

 producing plant to local supply depots or to local jobbers, or even 

 to veterinarians, it is not kept under the best possible conditions. 

 The effect of temperature and other factors upon commercial virus 

 is therefore being studied. 



A study of the relation of Bacillus suipestifer to hog cholera 

 as it occurs naturally and to the breaks in immunity which are 

 observed from time to time in immunized herds was continued and 

 two technical papers reporting results were published. 



The Biochemic Division produced about 50,000 cubic centimeters 

 of anti-hog-cholera serum for use in the various experiments and 

 also the virus required. Tests were made frequently of particular 

 samples of serum or virus alleged to be contaminated or worthless, 

 usually forwarded by the Division of Virus-Serum Control. Two 

 such lots of old defibrinated blood serum were tested, and both ap- 

 peared to be of undiminished potency. One sample of clear serum 



