Contagious Pleuro-Pneumonia of tlie Ox. 4G1 



resort to special pleading to give force to the evidence. The 

 experiment either fails, or the disease is developed in a form 

 which can be identified without hesitation. 



Doubts and disputes as to the existence of pleuro-pneumonia 

 cannot be determined in this way. Contagious lung-disease of 

 cattle cannot be produced by inoculation with the exudate from 

 a diseased lung. Thousands of cattle have been inoculated ; 

 large quantities of the morbid products of the disease have been 

 introduced into the system, not only by means of puncture, but 

 by deep incisions ; portions of a diseased lung have been placed 

 under the skin of a healthy animal and retained there, and yet 

 no development of lung-disease has resulted ; the effects pro- 

 duced have always been confined to the part in the first instance, 

 and when the local disease has extended to the adjacent tissues, 

 causing their destruction, the special site of pleuro-pneumonia, 

 the lung-tissue, has still remained unaffected. Death from the 

 poisonous action of the virus has followed in repeated instances, 

 but the animals thus killed by the virus of lung-disease have 

 always presented the anomaly of healthy respiratory organs. 

 Nothing in these statements admits of doubt or discussion ; the 

 facts are universally accepted. So far as our present means of 

 observation extend, we are justified in asserting that inoculation 

 with the matter of pleuro-pneumonia, as ordinarily practised, 

 produces local inflammation, followed by exudation, into the 

 tissues, of a fluid Avhich is identical in its characters and pro- 

 perties with the fluid exuded from the diseased lung ; both being 

 identical in their microscopic structure with the serum of healthy 

 blood in which putrefactive changes have commenced. 



It is objected with good reason that inoculation with the virus 

 of cattle-plague, sheep-pox, and foot-and-mouth complaint, is 

 dangerous to the stock in the vicinity of the inoculated animals. 

 From the centres thus intentionally established the disease may 

 spread to other herds and flocks which are not protected from 

 the infection. No such objection can be urged against inocula- 

 tion with the matter of pleuro-pneumonia. The most violent 

 advocates of the operation have never suggested that a cow which 

 has been inoculated is as likely to communicate the disease as 

 one which is suffering from the natural affection, or is indeed more 

 dangerous than a perfectly healthy uninoculated animal would be. 



The failure of all experiments to produce pleuro-pneumonia 

 by the introduction of the morbid products of the disease into 

 the areolar tissue beneath the skin led to the more severe opera- 

 tions of injecting the fluid into the structure of the lungs, into 

 the bronchial tubes, and also into the circulation and into the 

 digestive organs ; but before these experiments are referred to 

 it will be advantageous to describe the changes which occur 



