488 INFECTION AND RESISTANCE 



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 

 transmitted to cattle, and that it can be thus carried from animal to 

 animal, during this process becoming attenuated for human beings 

 to such a degree that reinoculated into man a simple vaccinia is 

 produced." 



Small-pox, therefore, represents in principle active immunization 

 by means of attenuated virus. When vaccination was first introduced 

 the virus was taken from preceding pustules produced in other human 

 beings. This has been given up in most countries to-day largely be- 

 cause of the dangers of transferring syphilis and other diseases in 

 this way. At present the method of obtaining virus for vaccination 

 purposes is carried out as follows: The initial material consists of 

 what is known as "seed" virus, which can be obtained from spon- 

 taneous cow pox or from vaccination pustules in children, or again 

 from pustules obtained in calves after several passages of small-pox 

 virus through these calves. From such seed virus calves may be in- 

 oculated for vaccine production or else the calves may be inoculated 

 from the material obtained from other calves in the usual way. 



Healthy young animals are used; they are washed along the 

 abdomen, strapped down upon specially prepared tables, and the 

 abdominal skin thoroughly cleansed with soap and water. The 

 exact procedure varies in different places; often the skin is thor- 

 oughly cleansed with carbolic solution, and this is thoroughly re- 

 moved with sterile water before inoculation, or else cleansing is 

 relied upon without the use of germicides. Over the clean area 

 longitudinal scratches 1 to 2 c. c. apart are made, and into these 

 the seed virus is rubbed. The animals are then kept in a clean 

 stall, preferably over asphalt floors, and rigid cleanliness is observed 

 during the period of development of the pustules. After the 6th or 

 7th day, when the vesicles are beginning to appear, the abdomen is 

 well washed and cleansed of superficial dirt without the use of an 

 antiseptic, and the pulp removed from the lesions with a curette. 

 The pulp so removed is placed into 60 per cent, glycerin and thor- 

 oughly ground up in a specially constructed mill. According to 

 Rosenau, the animal should always be killed before the vesicles are- 



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



