PLEURO-PNEUMOXIA. 171 



surface is much thickened, the exudate being both within and 

 upon the serous membrane. Microscopically examined, as shown 

 in fig. 6, the diseased products have every appearance of being 

 of recent origin, the secondary or degenerative changes (6, b) 

 which occur very early in pleuro where the blood supply is cut 

 off by plugging of the blood-vessels, having only commenced. 

 The history of the animal from which the specimen was obtained 

 was clearly traced. It had been brought from a healthy herd 

 six weeks prior to slaughter, throve and milked well up to the 

 two days prior to slaughter, when it presented slight signs of 

 illness, became rapidly worse, and when examined clear evidence 

 was obtained that both lungs were gravely invaded. I may 

 state that, along with four others, all of which succumbed, the 

 animal had been brought into a byre where the disease had 

 previously prevailed, but which had been declared free under 

 the Act of 1868. Taking into consideration the clinical fact, 

 which has forced itself upon me upon many occasions, that it 

 generally takes from a month to six weeks for the disease to 

 develop in a healthy animal introduced into an infected byre, 

 and the condition of the diseased products in the above case, 

 one cannot help concluding that pleuro-pneumonia is often a 

 very acute disease, and that it may rapidly involve large tracts 

 of lung tissue. 



In other instances, however, the invasion is confined to small 

 areas ; the disease may then assume a mild type, and the 

 animal recover; whilst in others the disease becomes chronic, 

 the animal dying, not so much from destruction of lung struc- 

 ture, but from a mal-condition of the whole system, arising 

 from absorption of the degraded products of the inflammation. 



The cause of pleuro-pneumonia, in this country at least, is 

 undoubtedly contagion and infection, and these only. My ex- 

 perience of the disease enables me to state that no mismanage- 

 ment with regard to feeding, housing, or the general treatment 

 of stock, will induce an outbreak of pleuro-pneumonia con- 

 tagiosa. 



I do not say, with some writers, that it nowhere originates 

 spontaneously; but I do say that it never originates spon- 

 taneously in this country. 



