738 INFECTION AND IMMUNITY. 



one first infected directly from the cow (cited 

 from S. W. Abbott). 



For at least half a century following Jenner's 

 discovery humanized lymph was used for vacci- 

 nation, new patients being inoculated by means 

 of points prepared from vesicles of previous cases, 

 or with the fresh lymph from such cases. The not 

 infrequent transmission of syphilis by this means 

 was the source of many calamities. Following the 

 precedent of Warlemont in 1868, the lymph of 

 cowpox is now the universal source of vaccine. 



Cowpox probably occurs to a greater or less 

 degree in all countries, especially in the spring and 

 summer,, attacks the udder and teats almost ex- 

 clusively, and is accompanied by very mild con- 

 stitutional symptoms. The incubation period is 

 from three to eight days. There is first local 

 heat, swelling and tenderness, followed by the for- 

 mation of papules, which in three or four days 

 after their appearance are transformed into vesi- 

 cles. The disease reaches its maximum develop- 

 ment at the tenth or eleventh day, the umbilicated 

 vesicles going through the usual course to crust 

 formation. 



Calves and heifers from the age of two months 

 to two years are best suited for vaccination in the 

 production of lymph for commercial purposes. 

 The region of the flank or the whole ventral sur- 

 face of the body may be inoculated, and in the lat- 

 ter instance as many as a hundred or more inser- 

 tions may be made. The skin is first shaved, 

 cleansed with antiseptics, and the lymph from an- 

 other calf is introduced by means of a syringe or 

 by scarification. In some institutions long, very 

 superficial parallel incisions are made and the 



