86 Manual of Veterinary Microbiology. 



through the rabbit, increases in volume; the bacillus 

 of the pyocyanic disease presents itself, according 

 to the media in which it is cultivated, as a bacillus, 

 a spirillum, or a micrococcus; the bacillus of gan- 

 grenous septicaemia grows in the form of short rods 

 in the connective tissue, in long filaments in the 

 serous membranes and blood. The bacteridium of 

 charbon, cultivated in bouillon containing a small 

 quantity of bichromate of potassium, loses its power 

 of forming spores, subsequent generations to which 

 it gives birth being also asporogenous. A tempera- 

 ture of 42° to 43° produces the same efllect upon the 

 bacteridium. 



The functional variations are of more importance ; 

 the pyocyanic bacillus, placed under certain condi- 

 tions, ceases to secrete the coloring matter which 

 characterizes it. There are, however, variations of 

 virulence w^hich more especially interest us. The 

 virulence of pathogenic germs may be increased or 

 diminished, then brought back to its normal intensity, 

 by conditions which vary with each microbe ; these 

 conditions will be considered more in detail in the 

 following paragraph. 



The virulence of a microbe may become enfeebled 

 to such an extent as to completely lose its pathogenic 

 powers ; it then becomes saprogenic. From the rec- 

 ognition of this fact to the admission of microbic 

 transformation there is only a step, j^evertheless, 

 up to the present, we have not observed the forma- 

 tion of a new species at the expense of another 

 Bpecies. From a practical point of view, however, it 

 must be admitted that certain saprogenic species may 



