BUEEAU OF ANIMAL INDUSTRY. 375 



had been begun. It was also reported that a study of the immunity 

 possessed b}^ the offspring of immune animals was likewise being con- 

 tinued. A brief report of the progress in these two lines of investi- 

 gation will now be presented, and certain other work which was 

 begun subsequent to the last annual report will be described. 



PBESEBVATION OF HOG-CHOLEBA VIRUS BY MEANS OF CHEMICALS. 



It is very desirable to be able to preserve hog-cholera virus by 

 means of chemicals without reducing its virulence. What is needed 

 is an antiseptic that will destroy all adventitious organisms witliout 

 affecting materially the virulence of the filterable virus of hog cholera. 

 The antiseptics employed in the experiments were phenol, formalde- 

 hyde, and thymol. 



I have previously reported that phenol could be added to the 

 defibrinated blood from hogs sick of hog cholera and containing the 

 virus of the disease without materially affecting the virus. Further 

 experiments have shown that a 1 per cent solution of phenol does not 

 destroy the virulence of hog-cholera blood after a contact of four 

 weeks, the preserved virus being kept during this time at a tempera- 

 ture of 6° C. Pathogenic bacteria, such Bacillus suipestifer, which 

 are frequently found in the blood of sick hogs, were in all cases de- 

 stroyed at the end of two weeks, and generally very much sooner, by 

 1 per cent of phenol. Simultaneous inoculations made by the use 

 of serum with virus containing 1 per cent of phenol appear to confer 

 an immunity which is quite as lasting as that secured when the un- 

 carbolized virulent blood is employed with the serum. 



Formaldehyde in the proportion of 1 to 10,000 and 1 to 12,000 

 (equivalent to approximately 1 to 4,000 and 1 to 5,000, respectively, 

 of the ordinary 40 per cent aqueous solution of formaldehyde) was 

 found to destroy all of the ordinary bacteria in the virulent defibri- 

 nated blood within two weeks, although the virus of hog cholera ap- 

 peared to be unaffected even after four weeks' contact. All speci- 

 mens were preserved during the experimental period at a temperature 

 of 6° C. No simultaneous inoculations were carried out with 

 formalized blood. 



Thymol was employed, as a rule, by adding one-half gram of the 

 thymol crystals to 100 cubic centimeters of blood. The thymol did 

 not appear to be as effective as either phenol or formaldehyde in 

 destroying the ordinary bacteria found in blood taken from sick 

 hogs, though usually at the end of four weeks the virulent blood to 

 which thymol had been added was found to be free from visible 

 bacteria. The thymol did not appear to have any noticeable effect 

 upon the virulence of the hog-cholera virus. 



Of the three preservatives the 1 per cent solution of phenol appears 

 to be the most effective as a preservative agent, and is therefore the 

 substance best suited for jirosorving virus for simultaneous inocula- 

 tions. On the other hand, however, the phenol is, of course, quite 

 toxic, and for this reason can not be used to preserve large amounts 

 of virus which are to be used later for hyperimmunization. In the 

 process of hyperimmunization such largo amounts of defibrinated 

 virulent blood must be injected that phenol can not be considered, 

 owing to the fact that the injected hog would almost certainly be 

 fatally poisoned by it. We have, however, employed certain lots of 



