THE MANUFACTURE AND USE OF SERA AND VACCINES. I39 



escape of serum, not actual bleeding. This scarified surface is then inoc- 

 ulated with glycerinated small-pox virus taken from a patient. When the 

 inoculated material has had time to be absorbed the animal is righted again 

 and cared for under as aseptic conditions as possible. In time (six to 

 seven days) pustules form over the entire inoculated area. The virulent 

 virus from man conve/s the disease to the animal, but in its passage through 

 the animal it becomes modified, losing in virulency, yet capable of producing 

 immunity as the result of a mild intoxication (vaccinia) . 



C. Removing the Scab. — The animal is again fastened to the frame. 



Fig. 62. — Showing the heifer strapped to the frame, preparatory to removing the 

 vaccinia scab from the area which was scarified and inoculated with the small-pox virus. 

 The scab patches show dark. 



The inoculated surface is vrashed and dried. The thick scab which has 

 formed over the inoculated area is then removed and triturated with 50 per 

 cent, glycerin. This constitutes the small-pox vaccine. 



D. Aging or Ripening the Vaccine. — The fresh or raw vaccine is not used 

 as it contains various living microbes. It is acted upon by the glycerin 

 added, for five or six weeks. The virus is tested bacteriologically during 

 this period, and as soon as no more colonies appear it is ready for use. 



E. Preparing for the Market. — The vaccine is now put into small glass 



