486 BACTERIOLOGY. 



culture over the entire surface. The growth, as a rule, can easily be 

 removed by adding- sterile water, and then gently agitating the 

 liquid. The thick suspension can then be poured out into sterile 

 flasks or drawn up into sterile bulb pipettes (p. 457). 



To measure out a dose of the growth Pfeiffer employs a small 

 loop (Oese) that will hold about 2 mg. of the material. This would 

 correspond to a loop about 1 mm. in diameter. A loopful of the 

 growth is stirred up into 1 c.c. of bouillon. A fraction of a loop, as X> 

 is obtained by transferring- 1 loopful to 4 c-c. of 

 bouillon and then taking- 1 c.c. of the suspension. 

 For the preliminary injections, it is advis- 

 able to employ dead cultures. The suspension 

 can be heated for 1 hour at 58-65, or it may be 

 shaken up with a few drops of chloroform. If 

 living cultures are employed, the dose for the 

 first injection must be a very small fraction of 

 the minimum fatal dose. A record must be kept 

 of the temperature and weight of the animal, 

 and, at no time, must an injection be repeated 

 suffa G c'e 6 ?ult?re U s X flask for before the temperature and weight have returned 

 to the normal. The first effect of an injection is 



to -cause a slight elevation of temperature which is followed by a 

 depression. The temperature may fall to 30 or lower, before death 

 occurs. The animal likewise loses considerably in weight. 



Cholera. Pfeiffer immunized guinea -pigs by injecting 

 into the peritoneal cavity one-third of an agar culture, 

 sterilized by chloroform or by heating at 65. Seven to ten 

 days later, about half a loopful of the living culture is in- 

 jected in the same manner. After a like interval, one loop- 

 ful of the living culture is injected; then, when the animal 

 recovers two loopsful can be given. In this way the dose 

 can be progressively increased till lasting immunity is ob- 

 tained. Guinea-pigs can thus be immunized so as to with- 

 stand 50 or 75 times the fatal dose. 



When the guinea-pig has acquired considerable resist- 

 ance a large dose of the cholera vibrios should be injected 

 into the peritoneal cavity. A few minutes later, a drop of 

 liquid should be removed from the cavity by means of a 

 drawn-out capillary tube (Fig. 62 c), and examined at once 



