472 Observations on Inoculation ivith the Virus of 



sufficiently numerous to afford a basis for the formation of a 

 positive opinion. 



Many of the statements which have been advanced relative 

 to the effects of inoculation have no practical significance, on 

 account of their negative character or their vagueness. The 

 assertion so commonly made that inoculated herds have re- 

 mained free from disease for a long period, is equally true if 

 applied to uninoculated herds ; and in both cases the truth is 

 valueless because negative. If in either instance it could be 

 shown that the animals had been exposed to infection, the 

 circumstances would be materially altered ; but this important 

 qualification is seldom thought of. Again, considering the dif- 

 ferent methods of operating, the degrees of skill on the part of 

 the operators, and the different kinds of material which are em- 

 ployed, it is difficult to believe that even a majority of the 

 animals submitted to the experiment have been effectually inocu- 

 lated. Some persons use a mixture of the exudate with glyce- 

 rine, a compound which may safely be deemed inert ; and yet 

 we do not hear that the results are less satisfactory than when 

 the undiluted fresh fluid is employed. 



All these circumstances account for the great differences of 

 opinion which prevail among scientific and practical men on 

 the subject of inoculation as a preventive of lung-plague, and 

 make it more than ever necessary that the attention which has 

 been recently excited should not be allowed to decline with- 

 out result. The problem is susceptible of solution in two ways. 

 First, by exposing a number of inoculated and uninoculated 

 cattle to the infection, and secondly, by inoculating a number 

 of herds in which pleuro-pneumonia has appeared, while an 

 equal number is left uninoculated under precisely similar con- 

 ditions. Both these tests may be applied at the same time ; 

 but if one be selected, the first is to be preferred, as being more 

 definite in its character and less complicated in details. 



Description of the Methods proposed for testing the 

 Efficacy of Inoculation with the Virus of Pleuro- 

 pneumonia. 



In order to carry into effect the first experiment of exposing 

 inoculated and uninoculated cattle to the contagium of pleuro- 

 pneumonia, it would be economical and in every way advan- 

 tageous to obtain some which had been inoculated by a skilled 

 operator twelve months, and others about three months, before 

 they are placed in contact with diseased animals. Failing this, 

 it would be necessary to devote a period of at least three months 

 to the performance of inoculation. 



