428 PROTECTIVE INOCULATION FOR BOVINE PLEURO-PNEUMONIA, 



virulent form of the disease. After this local afi'ectiou is over, the 

 animals are said to be proof against lung-plague. 



From this generalising report on the mode in which protective 

 inoculation for the cattle-disease under treatment is being prac- 

 tised, you will at once perceive its peculiarities. Take as object 

 of comparison the ideal of the modern preventive inoculations, 

 vaccination against variola. Vaccination in the human species is 

 admittedly followed by the intended result only when it is carried 

 out before the disease (variola, small-pox) has taken possession of 

 the individuals that are to be protected. It is a genuine preventive 

 treatment which will not admit of the incursion of the disease. 

 The same principle is adhered to in the preventive inoculations for 

 <;ertain animal plagues, for anthrax or splenic fever in sheep and 

 •cattle, for symptomatic anthrax (or " black-leg " or "quarter-ill ") 

 in cattle, for fowl-cholera, and swinefever. In all these cases the 

 ■employment of the preventive precedes, must precede the appear- 

 ance of the respective disorder, and not the other way. The ordinary 

 method of protecting cattle against " pleuro," however, does not 

 always seem to be guided by that principle. We have briefly 

 mentioned that inoculation will be performed after the plague 

 has already commenced its work. This being the case we are well 

 justified in assuming that, besides quite normal and healthy indi- 

 viduals, some, be they few or many, which have already taken up the 

 virulent agents of the disease, will be inoculated. Such an event 

 •could have occurred without having set up any reliable symptoms. 

 It must be remembered that, the auscultation of a bovine chest 

 being in itself no easy task, especially for non-experts, the difficul- 

 ties must accumulate when a cattle-owner has to inoculate, say, 1,000 

 head. The risk of inoculating individuals already but inperceptibly 

 infected, is moreover enhanced by our not knowing anything 

 exact about the period of incubation, and the precise course of the 

 disease. Yet it would appear as if the period of incubation is 



