282 Seventeenth Annual Report of the 



nearly the same time. When this characteristic is lacking sus- 

 picion as to the true nature of the disease should enter and we 

 should look carefully for special conditions which would explain 

 the delay in the eruption in individual cases. 



Another point no less characteristic is the appearance of the 

 eruption on the three primary points of election, on the mouth, feet 

 and in cows on the teats. A single animal, or a few, may show it 

 on but one or two of these points, hut, in a considerable herd, it 

 will be distributed among the three centers named, and in many, or 

 in the majority, more than one of these points "will be found to be 

 the seat of eruption in the same animal. 



From the eruption of cowpox it is easily distinguished by the 

 fact that the blister when formed is evenly rounded and is consti- 

 tuted by a single undivided internal chamber filled with a straw 

 colored liquid, and can be completely evacuated through the open- 

 ing made by a single prick of a fine needle. The cowpock, on the 

 other hand, may fail to form a distinct blister on a surface which 

 is densely covered by hair, where it gives rise rather to an exudate 

 which concretes on the surface into a more or less dense crust. 

 When, as on the hairless skin of the teats, it does form a vesicle, 

 the latter is depressed or " pitted ' in the center, so that the 

 external bulging margin forms a ring. Then, again, the interior- 

 forms not one but several chambers, so that if pricked by a needle 

 the lymph escapes only from the chamber penetrated and several 

 pricks are necessary to evacuate all the liquid. These distinctions 

 are the more important as the diseases are both mild and attended 

 by a slight transient fever, the period of latency (incubation) is 

 nearly the same, and the duration of the two diseases is about 

 equal, favorable cases of cowpox having completely recovered by 

 the twentieth day. The tendency of the aphthous fever, however, to 

 attack the mouth and, above all, the interdigital arch between the 

 hoofs clearly distinguishes that from cowpox. Cowpox generally 

 affects milch cows only, and usually when they are first introduced 

 into an infected herd. As a rule it is confined to the teats, and 

 spares steers, bulls and heifers not in milk, as also exposed sheep 

 and swine. Foot and mouth disease, on the other hand, rarely fails 

 to affect the feet, and as the contaminated feet infect the ground, 

 neither sex, the unimpregnated condition, the absence of milk secre- 



