490 INFECTION AND RESISTANCE 



and Otto found that the immunization of animals with large doses 

 of killed agar cultures of plague bacilli and with Haffkine's prophy- 

 lactic did not protect them against subsequent inoculation with viru- 

 lent cultures. 



Strong 96 subsequently made a very careful comparative study of 

 the various methods of plague vaccination, and concluded that the 

 most efficient method is immunization with attenuated living cul- 

 tures. He showed that when carefully done this method can be 

 safely employed in human beings, but admits that his work must be 

 as yet considered as experimental and further studied before it can 

 be universally employed. 



Besredka 97 has advised the use of sensitized dead plague cul- 

 tures, claiming, from animal experimentation, that such vaccines 

 produce an efficient and relatively durable immunity. 



Rowland 98 confirms the immunizing properties of Besredka's 

 vaccines in plague, and believes that the antigenic properties of the 

 plague bacillus are attached to the bacterial nucleoproteins, and can 

 be extracted with these. Rowland prepares a vaccine by the treat- 

 ment of the moist bacteria with enough anhydrous sodium sulphate 

 to combine with all the water present, freezing and thawing the 

 mixtures, then filtering off the bacterial deposits at 37 C., and ex- 

 tracting them with water. The solution so obtained was fatal to 

 rats in small quantities and afforded substantial protection, reducing 

 the mortality on subsequent inoculation of a standard culture from 

 80 to 10 per cent. 



PROPHYLAXIS AGAINST SMALL-POX 



In the case of small-pox the general method of active prophylactic 

 immunization is in principle identical with that devised by Jenner 

 in the 18th century. The original observation from which Jenner 

 worked was that dairy maids and other individuals who had been 

 infected with cow pox were thereafter spared when a small-pox epi- 

 demic appeared in the region in which they lived. It is now agreed 

 by most observers who have studied the problem that the virus of cow 

 pox and that of small-pox are identical in nature ; the former repre- 

 senting a strain attenuated by passage through the animal body. This 

 is based chiefly upon the observation that true variola can be trans- 

 mitted to cattle, and that it can be thus carried from animal to ani- 

 mal, during this process becoming attenuated for human beings to 

 such a degree that reinoculated into man a simple vaccinia is pro- 

 duced. 99 



96 Strong. Journ. of Med. Ees., N. S., 13, 1908. 

 87 Besredka. Bull, de I'Inst. Past., Vol. 8, 1910. 



98 Rowland. Journ. of Hyg., Vol. 12, 1912, p. 344. 



99 Haccius. Cited from Paul, Kraus and Levaditi, Vol. 1, p. 593. 



