SMALLPOX 



185 



is placed in a suitable receptacle, weighed and treated with five 

 times its amount of sterile glycerin-water (80 parts of glycerin and 

 20 of water). The quantity which can usually be obtained from one 

 animal varies between 25 and 50 grams (in the case of retrovaccine 

 of the second generation). Twenty-four hours after the removal 

 of the material the animal is killed, and if no disease that could 

 affect the vaccine is found postmortem, this is further treated as 

 follows: After standing for two weeks in contact with the glycerin 



Belly of heifer, showing one of the modern methods of propagating vaccine virus; lesions photo- 

 graphed at the end of five days. (Taken from Welch and Schamberg.) 



the mixture is thoroughly triturated in a "lymph mill," when the 

 resultant emulsion is filtered through gauze and is then stored for 

 at least three or four weeks at a temperature of 8 C., the idea being 

 to favor the destruction by the glycerin of contaminating micro- 

 organisms, the admixture of which is practically unavoidable, even 

 though the field of operation be ever so carefully protected. 



If a bacteriological examination then shows the presence of but 

 few (e. g., less than 30 per 0.01 c.c.) and the absence of all suspicious 

 organisms, including the tetanus bacillus (the latter point is tested 



