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XVIII. — Observations on Inocnlation icith the Virus of Contagious 

 Pleuro-Pneuvfionia of the Ox, chiefly in reference to the local 

 and systemic Changes ichich are induced. By G. T. BrowN, 

 Professor of Physiology in the Royal Veterinary College, and 

 Chief Inspector to the Veterinary Department of the Privy 



Council. 



[With Four Plates.] 



Inoculation with the products of an infectious or contagious 

 disease must, in the first instance, have been a purely speculative 

 proceeding. There is absolutely nothing in the natural history 

 of contagious maladies which suggests the probability of an 

 attack assuming a milder form when the poison is introduced arti- 

 ficially into the svstem, than when it obtains an entrance in the 

 ordinary wav while sick and healthy animals are herded together. 



It is quite conceivable that the chief intention of the operator 

 was to facilitate the progress of a disease, which experience taught 

 him was almost certain to attack all the animals within its reach, 

 and thus to concentrate the results in a short space, instead of 

 permitting them to extend over an indefinite period. Nothing 

 would be lost by this measure in any case, and at least time 

 would be gained, while the recovered animals would be pro- 

 tected from a second attack to the same extent as they would be 

 if the affection had been taken naturally. There would be one 

 further result, which to most minds would appear a manifest 

 advantage, the avoidance of suspense, at the cost of precipitating 

 the impending mischief. Observation, it may be imagined, 

 would soon establish the important facts which are now fully 

 realized, viz., the milder character of the inoculated disease, the 

 shortening of the period of incubation, and the marked influence 

 of sanitary conditions on the course of the malady. Small-pox 

 was most probably the first disease which was intentionally 

 transmitted by inoculation with perfect success as far as the 

 individual was concerned, but with disastrous results to the 

 unprotected persons who came in contact with him. The sub- 

 stitution of the vaccine virus, which is the small-pox poison 

 passed through the system of the ox, at once removed the objec- 

 tion which was urged against inoculation, and provided a sale 

 remedy for a deadly disease. 



Among the lower animals, cattle-plague, foot-and-mouth 

 disease, and sheep-pox, have been made the subjects of experi- 

 ments in inoculation with varying i-esults. The virulent cattle- 

 plague occasionally loses something of its deadliness when arti- 

 ficially induced ; but the degree of risk to the animal operated 

 on, and also to others in its vicinity, is too high to encourage 



