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taken that it is not contaminated with blood. With practice the 

 vesiculated epithelium can be removed in long strips. The material 

 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 retro- vaccine 

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

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



FIG. 11 



Belly of heifer, showing one of the approved modern methods of propagating vaccine virus; 

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



affect the vaccine is found post mortem, this is further treated as 

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

 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 



