34 VACCINE AND SERUM THEEAPY 



a second inoculation be given during the negative 

 phase, grave harm may be done ; even the life of the 

 animal may be endangered. 



We have seen that the immune bodies established 

 in the serum of an animal are specific for the bacteria 

 employed in the immunisation ; it is, therefore, 

 obvious that, to have good results in vaccine therapy, 

 it is absolutely necessary to employ a vaccine made 

 from the specific organism causing the disease. This 

 may not only apply to species, but to individual 

 organisms of the species. 



The proper course, therefore, to pursue is to employ 

 an autogenous vaccine, but in some diseases — for 

 instance, those caused by the streptococcus and 

 staphylococcus — we may have a mixed infection of 

 the cocci bacilli, some of which may be practically 

 avirulent. In order, therefore to produce a suitable 

 vaccine to combat the disease, we must determine 

 which of the organisms found in the lesions are the 

 highly virulent ones, and to prepare the vaccine from 

 those. In infections where there is a mixed variety 

 of bacteria, and we are not certain which type is 

 causing the disease, the proper policy to pursue is to 

 make a vaccine of each type, or, in other words, a 

 mixed vaccine. The use of commercial vaccines in 

 the treatment of diseases is in most cases useless, as 

 they seldom or never contain the specific organism 

 producing the disease. 



Leucocyte Extract. — In the preceding paragraphs 

 upon opsonins and phagocytosis is discussed the 



