PATHOGENETIC PROPERTIES 315 



PATHOGENESIS. 



Living Bacteria. 



(a) Psychrophilic Bacteria : When the organism will 

 only grow at or below 18 to 20 C., 



1. Prepare cultivations in nutrient broth and in- 

 cubate under optimum conditions. 



2. After seven days' incubation inject that amount 

 of the culture corresponding to i per cent, of the 

 body-weight of a healthy frog, into the reptile's dorsal 

 lymph sac.. 



3. Observe until death takes place, or, in the event 

 of a negative result, until the completion of twenty- 

 eight days (vide Chapter XVIII). 



4. If, and when, death occurs, make a careful post- 

 mortem examination (vide Chapter XIX) . 



(b) Mesophilic Bacteria: When the organism grows 

 at 3 5 to 3 7 C., 



1. Prepare cultivations in nutrient broth and incu- 

 bate under optimum conditions for forty-eight hours. 



2. Select two white mice, as nearly as possible of 

 the same age, size, and weight. 



3. Inoculate the first mouse, subcutaneously at 

 the root of the tail, with an amount of cultivation 

 equivalent to i per cent, of its body- weight. 



4. Inoculate the second mouse intraperitoneally 

 with a similar dose. 



5. Observe carefully until death occurs, or until the 

 lapse of twenty-eight days. 



6. If the inoculated animals succumb, make com- 

 plete post-mortem examination. 



If death follows shortly after the injection of cul- 

 tivations of bacteria, the inoculation experiments 

 should be repeated two or three times. Then, if the 

 organism under observation invariably exhibits patho- 

 genic effects, steps should be taken to ascertain, if 

 possible, the minimal lethal dose (vide infra) of the 

 growth upon solid media for the frog or white mouse 



