82 Manual of Veterinary Microbiology. 



has been incidentally given in connection with the 

 subject of their pathogeny. We will only say a few 

 words on the specificity of pathogenic microbes. At 

 an early period in bacteriological research investi- 

 gators applied themselves to the discovery of a spe- 

 cial microbe for each disease ; it was believed that 

 every germ produced always the same efiects. We 

 now know, however, that the same microbe may give 

 rise to very diiferent diseases : the microbe of fowl 

 cholera gives a true septicaemia in the rabbit, a cir- 

 cumscribed abscess in.the guinea pig; the streptococ- 

 cus pyogenes develops sometimes an abscess, some- 

 times an erysipelas, sometimes puerperal fever. Sim- 

 ilarly, a given lesion may be consecutive to the inoc- 

 ulation of dilFerent microbes : the particular inflam- 

 matory lesion which has received the name of tuber- 

 cle has for. its usual cause the tubercle bacillus; but 

 other agents can develop identical changes, which 

 have been designated pseudo-tubercles in order to dis- 

 tinguish them from those in which the said bacillus 

 exists ; among the number of these agents we may 

 mention croton-oil, lycopodium spores, the demodex 

 folliculorum, strongylus vasorum, the utricular sarco- 

 spermia of the muscles of the pig, the actinomyces, 

 the pseudo-tubercle bacillus of Courmont, etc. Ty- 

 phoid fever of the horse appears to develop under the 

 influence of various species of microbes, acting inde- 

 pendently. 



Microbic specificity is, therefore, not absolute; it 

 depends upon the organism in which the parasite 

 has implanted itself and on the external conditions 

 which may have influenced the latter. Attenuation 

 of a microbe suffices, indeed, to change its effects. 



