THERAPEUTIC IMMUNIZATION IN MAN 491 



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 re- 

 lied 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 

 removed, not only for humane reasons, since the same object might 

 be attained with anesthesia, but because a thorough autopsy can then 

 be performed to determine the health of the calf. 



Vaccines so obtained always contain bacteria, the glycerin there- 

 fore serving a double purpose : one, the preservation of the virus, the 

 other a gradual destruction of the bacteria. Rosenau has shown that 

 the addition of 2 to 4 parts of 60 per cent, glycerin to one part 

 weight of the pulp prevents the growth of bacteria and probably 

 destroys them by dehydration. Most of the bacteria are destroyed 

 within one month at 20 C. During this period, then, from 4 to 6 

 weeks, the glycerinated virus should not be used, and should from 

 time to time be controlled by cultivation. At the end of this time 

 the lymph is ready for use. 



Formerly the material for the vaccination of human beings was 

 obtained very simply by dipping ivory splinters into the fluid of pus- 

 tules, allowing this to dry, and rubbing these ivory or bone points 



