328 INFECTIVE DISEASES. 



from the phenomena of an ordinary vaccination, but that does not 

 mean that they produced the disease cow-pox. The vesicle which 

 followed the inoculation, whether papular or vesicular, was small-pox. 

 Ceely, Badcock, Yoigt, and others, succeeded in ingrafting the cow 

 with small-pox, and when suitable lymph and suitable subjects were 

 employed, the virus was so attenuated that a benign vesicle resulted. 

 Similar results were obtained by Sutton and Dimsdale, and identical 

 results by Adams, Guillou, and Thiele, by inoculating the human 

 subject with variolous lymph without first ingrafting the disease on 

 the cow. 



Vaccination with variola-vaccine is simply a modification of the 

 Suttonian system of small-pox inoculation, only in the first remove 

 the cow is substituted for the human subject. All those who were 

 inoculated with Ceely's, Badcock's, or Simpson's variola-vaccine, 

 were not in the usual meaning of the word vaccinated ; they were 

 not inoculated with cow-pox but they were variolated, and in such 

 an extremely attenuated form that the persons so variolated do 

 not convey the infection. By judicious selection it is thus possible 

 to obtain a strain of lymph from variola which, by direct inoculation 

 of the human subject or by first inoculating a cow, is deprived of 

 infectious properties, and produces on the arm the physical characters 

 of an ordinary vaccine vesicle. This has been regarded as a proof 

 of the identity of small-pox and cow-pox, but it is not so. Variola, 

 and cow-pox are not the only diseases caused by a virus which can 

 be attenuated until only a vesicle is produced with the characters of 

 an ordinary vaccine vesicle. The results which have been obtained 

 with the virus of cattle plague and of sheep- pox and horse- pox have 

 been given in previous chapters ; and no one would urge on this 

 account that human small-pox, cattle plague, cow-pox, sheep-pox, 

 and horse-pox are all manifestations of the same disease. Cow-pox 

 has never been converted into human small-pox, and, in their clinical 

 history and epidemiology, natural cow-pox and human small-pox 

 are so different, that the comparative pathologist is no more pre- 

 pared to admit their identity than he is prepared to admit the 

 identity of cow-pox and sheep-pox, or small-pox and cattle plague. 



Protective Inoculation. Whether vaccination of all heifers 

 on a farm would protect them from cow-pox when they came into 

 milk is not known, the duration of the immunity in calves afforded 

 by vaccination having not been determined. Calves undoubtedly 

 have an immunity after vaccination, lasting for some weeks. 



In 1896 Beclere, Chambon, and Meriard experimented upon 

 the immunising power of the serum of vaccinated calves. They 



