GENERAL CONSIDERATION OF FILTRABLE VIRUS 895 



obtained from the pustules of those previously vaccinated. While 

 this method was perfectly satisfactory for the immediate purposes 

 in view, practical difficulties and the occasional accidental trans- 

 mission of syphilis have rendered this practice undesirable. In 

 consequence, at all institutes at which vaccine is produced for use 

 upon man, the virus is obtained from animals. Horses and mules, 

 both extremely susceptible to vaccine, have been employed, and 

 goats have, at times, been chosen because of their insusceptibility 

 to tuberculosis. Rabbits have also been used more recently by Cal- 

 mette and Guerin. 13 



The animals almost exclusively employed at the present day, 

 however, are calves, preferably at ages of from six months to two 

 years. Very young suckling calves are unsuitable because of the 

 great speed of development and small size of the lesions produced.- 

 The animals should be healthy and at some institutes (Dresden) 

 are subjected, before use, to the tuberculin test ; although, according 

 to Paul, 11 this produces a hypersusceptibility to the vaccine, and 

 can be omitted without danger when careful supervision is observed. 

 Some observers prefer to use light-colored animals rather than dark- 

 skinned or black ones, both for reasons of greater ease of cleanliness 

 and because the former are supposed to be more susceptible than 

 the latter. This contention is denied by others. The sex of the 

 animals is immaterial. 



During the period of use, the calves are fed, according to age, 

 with either an exclusive milk diet, or they are given, in addition, 

 fresh hay. The greatest cleanliness in regard to the bedding and 

 stalls must be observed and separate stables should be available 

 for the animals under treatment and those under observation before 

 treatment. These stables, if possible, should be so built that they 

 can be easily scoured and flushed with water, and stalls should be 

 disinfected after occupation. If possible, stables should be artifi- 

 cially heated and a comfortable temperature maintained. Halters 

 and fastenings should be so arranged that the animals can not lick 

 the scarified surfaces. Careful veterinary control before vaccination 

 and during the period of treatment must be observed in order to 

 eliminate animals with systemic disease or other complications. 



The calves may be vaccinated with material taken from 

 previously vaccinated animals. Again, they may be inoculated with 



Calmette and Guerin, Ann. de 1'inst. Pasteur, 1902. 



