70 Ths Farmer's Veterina/ry Adviser. 



probability of the conveyance of germs on instruments or on 

 the person and clothes of the operator or his assistants. 



4:th. Then, too, as the practice is often called for in herds, 

 among which the plague in question has already appeared, 

 there is always the probability of the presence of germs on 

 the surface of the animal inoculated, and unless the skin is 

 first thoroughly cleansed and disinfected (say with chloride 

 of mercury, 1 to 1,000 water) such germs are liable to be car- 

 ried in with the instrument and deposited in the tissues. 



5th. In all such infected herds, too, a given number of 

 animals will usually have the germs already in their sys- 

 tems, and in such cases the sterilized virus, weakening the 

 vital resistance of the blood and tissues, will too often con- 

 tribute to intensify the already implanted disease. 



6th. With a general application of the principle it would 

 inevitably happen that blunders would be made by the 

 owners and others as to the precise nature of the disease to 

 be prevented, and thus the products of one plague would 

 be inoculated to prevent the irruption of another, and in 

 the consequent failure the whole system would receive un- 

 merited discredit. To avoid this, and in the absence of the 

 requisite skill for diagnosis, the virus should be obtained 

 from one of the victims in the herd, and prepared with all 

 due precaution on the spot. In such case a failure would be 

 unlikely, unless the subject furnishing the virus showed only 

 an imperfectly developed type of the malady, or unless two 

 diverse maladies existed in the same herd at the same time. 



7th. Another obvious precaution is to take virus only 

 from typical cases of the disease to be prevented, and not 

 from those which show any defect in development (as the 

 chemical products are then liable to be wanting in strength) 

 nor from advanced nor complicated cases (in which there 

 may be superadded germs of other poisons and other deadly 

 products). Thus in the advanced stages of disease the 

 propagation of septic germs is not at all uncommon. 



