VACCINE-THERAPY 151 



or an indirect effect of one or more species of bacteria or 

 their products no one can deny, but that the bacteriology 

 of the disease leaves a great deal to be desired we must 

 all admit. 



In cases of this kind a variety of micro-organisms have 

 been isolated from time to time, including diplococci, 

 staphylococci, streptococci, and bacilli, and, judging from 

 our present bacteriological knowledge, it is difficult to 

 ascribe to which microbe the production of the specific 

 blood-lesions belongs. 



When one is dealing with a simple catarrhal fever, an 

 attack of influenza (so called), or an outbreak of strangles, 

 in a stud of horses, the disease generally attacks one 

 animal first, the others slowly or suddenly developing the 

 affection. As the disease goes through the stable, one can in- 

 variably isolate, microscopically and biologically, the specific 

 microbe, or, in the case of mixed infections, microbes from 

 all the patients. As a sequel to the outbreak one animal 

 may develop purpura heemorrhagica, for in practice we 

 seldom see more than one case, the disease being very 

 sporadic, and all the others may make a good recovery. 



Why should this one animal be singled out for this com- 

 plication ? He has been under the same dietetic, hygienic, 

 and therapeutic management, and his constitutional health 

 and age before the illness began Was as good as the others 

 which recovered. Nay, more ; for all that we know the 

 clinical phenomena suggested that the specific infection 

 from which he was suffering was identical to the others 

 which recovered without this complication. 



We are now face to face with one of two facts : either 

 this animal has had, firstly, a hypervirulent dose, or, secondly, 

 his protective forces are so defective that, not only is he 

 unable to resist the invasion, but the specific invading 

 bacteria find in his economy the very essentials in the most 

 suitable proportion to suit their requirements. 



As regards the first hypothesis, it is scarcely tenable ; 

 for why should this animal be singled out for a more 



