252 BACTERIA 



affected with cow-pox, contracted in the discharge of their 

 duty as milkers, did not contract small-pox, even when 

 placed in risk of infection. Hence he inferred that inocul- 

 ation of this mild and non-infectious disease would be pre- 

 ferable to the process of variolation then so widely adopted 

 in England. Jenner therefore suggested the substitution of 

 cow-pox lymph (vaccine) in place of small-pox lymph, as in 

 ordinary variolation. 



It should not be forgotten that variolation was thus the 

 first work done in this country in producing artificial im- 

 munity, and was followed by vaccination, which was only 

 partly understood. Even to-day there is probably much to 

 learn respecting it. Both variolation and vaccination may 

 be described as active immunisation by means of an attenuated 

 form of the specific virus causing the disease. The nature of 

 the specific virus of both small-pox and cow-pox awaits dis- 

 covery. Burdon Sanderson, Crookshank, Klein, and Cope- 

 man have all demonstrated bacteria in cow-pox or vaccine 

 lymph, and in 1898 Copeman announced that he had isolated 

 a specific bacillus and grown it upon artificial media. 1 

 Numerous statements have been made to the effect that a 

 specific bacillus has been found in small-pox also. But 

 neither in small-pox nor cow-pox is the nature of the con- 

 tagion really known. 2 



These facts, however, do not remove the suspicion which 

 has hitherto rested upon vaccine lymph as a vehicle for bac- 

 teria of other diseases which by its inoculation may thus be 

 contracted. A few remarks are therefore called for at this 

 juncture upon the recent work of Dr. Monckton Copeman 

 and Dr. Frank Blaxall in respect to what is known zsglycer- 

 inated calf lymph. Evidence has been forthcoming to sub- 



1 An exhaustive account of vaccine may be found in the Milroy lectures 

 delivered in 1898 at the Royal College of Physicians by S. Monckton Cope- 

 man, M.D. 



2 Crookshank, Bacteriology and Infective Diseases ; Virchow, The Huxley 

 Lecture, 1898. 



