30 DEPARTMENT OF AGRICULTURE. 



openiiiff the air pnssaj;:os of this cow after deatli, they Avere found 

 throughout their whoU; extent nearly tiUed Avith a deposit siniiUir to 

 tliat usually found on the surface of the diseased luuff. 



There is little necessity for proloniifinij this <h'scription of cadaveric 

 manifestations. The heart's sac is sonietiuies thickened by dei)osits 

 around it. Not unfrequently it contains an excess of serum. The heart 

 itself is contracted and pale, containing- a little dark blood. The organs 

 of digestion at different stages manifest a state of dryness. The third 

 stomach, which is so constantly packed with dry food in febrile diseases, 

 is in the same condition in pleuropneumonia. 1 liave known the mu- 

 cous layers spotted with irregular or circular congestions or blood extra- 

 vasations, and the nuMiibrane softening in these parts has become per- 

 forated. In advanced cases there is more or less diffuse redness, and 

 even blood extravasations in the large intestine, with fluid, fetid and 

 sometimes slightly blood-stained excrement, such as is discharged during 

 life. 



The anfemia — or bloodless condition of other tissues — the dark, dry look 

 of the meat dressed by the butcher, the yellow color of the fat in some 

 cases, and the small quantity of fat left in animals that have succumbed 

 under a chronic attack, are all general signs of greater or less value, 

 when taken in conjunction with the changes occurring in the chest 



THE CAUSES OF TEE LUXG PLAGUE. 



The facts which have been adduced in the foregoing pages would seem 

 sufficient to set at rest discussions as to the causes hitherto alleged as 

 giving rise to the spontaneous development of contagious pleuro-pneu- 

 monia. Nevertheless we have seen that wherever the malady appears 

 for the first time the relation of its undoubted cause and effect is usually 

 overlooked. Many circumstances tend to obscure the observations even 

 of experts, and it is more i)arti(*ularly in large cities, where the disease is 

 most common and observers more numerous, that conditions mislead and 

 have misled. With a view therefore to impede the renewal of false 

 theories which have up to the present day insured the steady reproduc- 

 tion and propagation of this bovine pest, it may be well to enter into 

 details under three heads: 



1st. The alleged original causes of the lung plague. 



2d. Contagion and infection. 



3d. Conditions fa^'oring or insuring comnumication of the disease by 

 actual contact or approach. 



THE ALLEGED ORIGINAL CAUSES OF THE LUNG PLAGUE. 



Man at all times and in virtue of a strong instinct theorizes on the 

 why and the wherefore of everything. Valentini, in his records of the 

 lung disease, overlooking altogether many points which, with the know- 

 ledge of the present day, enable us to interpret correctly the phenomena 



