INFECTIOUS DISEASES OF CATTLE. 429 



of the human family is well known. The immunity which such vac- 

 cination confers upon the human subject has led many writers to 

 assert that cowpox is simply a modified form of smallpox, whose 

 harmless attack upon the human system is due to a certain attenua- 

 tion derived during its passage through the system of the cow or 

 horse. The result of numerous experiments, which have been car- 

 ried out for the purpose of determining the relationship existing 

 between variola of the human and bovine families, seems to show, 

 however, that although possessing many similar characteristics, they 

 are nevertheless distinct, and that in spite of repeated inoculations 

 from cattle to man, and vice versa, no transformation in the real 

 character of the disease ever takes place. 



Symptoms. — The disease appears in four to seven days after natural 

 infection, or may evince itself in two or three days as the result of 

 artificial inoculation. Young milch cows are most susceptible to an 

 attack, but older cows, bulls, or young cattle are by no means immune. 

 The attack causes a slight rise in temperature, which is soon followed 

 by the appearance of reddened, inflamed areas, principally upon the 

 teats and udder, and at times on the abdominal skin or the skin of 

 the inner surface of the thighs. In a few cases the skin of the throat 

 and jaws has been found similarly involved. If the affected parts are 

 examined on the second day after the establishment of the inflamma- 

 tion numerous pale red nodules will be found, which gradually expand 

 until they reach a diameter of one-half inch or even larger, within 

 a few days. At this period the tops of the nodules become trans- 

 formed into vesicles which are depressed in the center and contain a 

 pale serous fluid. They usually reach their maturity by the tenth 

 day of the course of the disease and are then the size of a bean. 

 From this time the contents of the vesicles become purulent, which 

 requires about three days, when the typical pox pustule is present, 

 consisting of a swelling with broad, reddened base, within which is an 

 elevated, conical abscess varying from the size of a pea to that of a 

 hazelnut. 



The course of the disease after the full maturity of the pustule is 

 rapid where outside interference has not caused a premature rupture 

 of the small abscess at the apex of the swelling. The pustules gradu- 

 ally become darker colored and dryer until nothing remains but a 

 thick scab, which at last falls off, leaving only a slight whitish scar 

 behind. The total duration of the disease covers some twenty days 

 in each animal, and, owing to the slow spread of the infection from 

 animal to animal, many weeks may elapse before a stable can be fully 

 freed from it. The fallen scabs and cruets may retain their conta- 

 gious properties for several days when mixed with litter and bedding 

 upon the floor of the stable, and during this period they are at any 

 time capable of producing new - outbreaks should fresh cattle be 

 brought into the stalls and thus come into actual contact with them. 



