94 BACTERIOLOGY 



introduced into the gullet in the case of rabbits, through 

 the gap between their teeth, in that of guinea-pigs, through 

 a small perforated gag clamped between the incisors the 

 bougie used being a soft elastic catheter. When it is 

 wished to infect an animal artificially the micro-organisms 

 must be introduced into the intestine, as the acid gastric 

 juice frequently impairs their vitality. 



Nicati and Eietsch in their experiments on cholera 

 injected the infecting liquid directly into the duodenum, 

 which they had laid bare by a laparotomy performed with 

 the strictest antiseptic precautions. Koch recommended 

 the following mode of procedure for the purpose of excluding 

 the injurious effect of the gastric juice on the micro- 

 organisms : A wooden gag perforated in the centre having 

 been introduced into the mouth of the animal, a sound is 

 inserted through it, and 5 c.crn. of a saturated solution 

 of sodium carbonate is injected to neutralise the acid gastric 

 juice. One grm. of tincture of opium for every 200 grms. of 

 body-weight is then injected subcutaneously, in order to keep 

 the animal in a state of narcosis, after which cholera-bacilli 

 suspended in bouillon are injected by means of an oesopha- 

 geal tube, and the experiment of introducing infection by 

 the intestinal canal is complete. 



Subcutaneous infection. Inoculation can also be per- 

 formed subcutaneously by introducing the infecting matter 

 beneath the skin with a Koch's syringe. In the case of small 

 animals, such as white mice, the hair of the back in the 

 neighbourhood of the tail is carefully removed, a minute 

 incision is made into the skin with disinfected instruments 

 (forceps and scissors), and the infecting matter introduced 

 subcutaneously with the help of a sterilised platinum loop. 



Experiments of transmission into the peritoneal and 

 pleural cavities, or into the organs themselves, are con- 

 ducted after a similar fashion. 



