CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 251 



a pasture that has beeu occuined by the latter, would hardly be possi- 

 ble, and, at the utmost, only one or a few animals of a herd would 

 contract the disease. Another theory charges the excrements of South- 

 ern cattle with constituting the vehicle of the pathogenic principle. 

 The objections just made against the urine theory will also dispose of 

 the dung theory; besides, all cattle, but particularly grown animals, 

 carefully avoid to graze where other cattle have deposited their excre- 

 ments. They are apt to sniff" at places where horses have voided their 

 ■dung, and when suffering from certain digestive disorders, attended 

 witli a vitiated appetite, may even eat some horse manure, but they 

 will never graze if they can help it where the dung of their own kiud 

 has been deposited, a fact well known to every cattleman. It may be pos- 

 sible that some pathogenic bacteria pass oft" with the dung, or even with 

 the urine; but if they do, they most assuredly do not furnish the princi- 

 pal source of infection. Another theory charges the hoofs of the Southern 

 cattle with being the communicators of the infectious principle. This the- 

 ory, too, can be easily disposed of, even if it were possible that the hoofs 

 were able to take up the pathogenic principle (bacteria, for instance), 

 at the native range, and convey it to some other place, that other place 

 could only be in the immediate neighborhood, because at every step in 

 the grass the hoofs are wiped, and in mud or water they are apt to 

 lose whatever may cling to them ; besides, neither the horn of the hoof 

 nor the skin of the foot constitutes the soil or medium needed for the 

 reproduction, preservation, and propagation of such a pathogenic prin- 

 ciple as that which causes the southern cattle fever. Even if the skin 

 of the foot, particularly in the cleft between the hoofs, constituted a 

 suitable medium, and att'orded all the conditions necessary to the exist- 

 ence and reproduction of the pathogenic principle, the constant wiping 

 and friction which those parts are subjected to on the march would pre- 

 clude the possibility of conveying the principle (bacteria) in that way 

 a thousand miles or even farther. Still another theory, which has yet 

 a great many adherents even among practical cattle-men, charges the 

 ticks often found on Texas cattle with being the bearers of the infectious 

 principle, or even with constituting themselves the pathogenic agency. 

 The principal objection that can be brought to bear against this theory 

 is the fact that Southern cattle free from ticks will infect Northern past- 

 ures, «&c., just as soon as those that have them, and that ticks of the 

 same kind also occur in countries in which the southern cattle fever 

 never originates or makes its appearance, unless it is introduced by 

 Southern cattle infecting a trail, pasture, water-hole, &c. The ]>erspi- 

 ration (through the skin) ol Southern cattle, and even the expirations 

 (from the lungs) have been accused of constituting the pathogenic prin- 

 ciple, or the vehicle of the same. ]5ut this theory, too, is fallacious, for, 

 if true, the pathogenic agency would be of a volatile nature, and be 

 communicated through the air, which it evidently is not, as already 

 -Stated, llence, the only thing that remains as the probable vehicle 



