﻿STUDIES IN PLAGUE IMMUNITY. 161 



However, both the German Plague Commission and Kolle have shown that 

 the immunizing substances in Haffkine's prophylactic are mainly contained in 

 the sediment consisting of the killed organisms. Kolle ° showed that the clear 

 fluid drawn off above the dead bacteria possessed but little immunizing power and 

 further demonstrated that the number of bacteria in the old bouillon cultures 

 was very small in proportion to the number that could be obtained in the same 

 volume of fluid if agar cultures were used. Thus, one agar culture contained 

 about as many bacteria as from 80 to 100 cubic centimeters of an old bouillon 

 culture. Obviously whatever immunizing power the clear fluid above the sedi- 

 ment possesses is due to the free receptors which have been separated from the 

 dead bacilli. It therefore seems evident that killed agar cultures are superior 

 for inoculation to the killed bouillon ones. 



Lustig and Galeotti in 1897 10 recommended the use of an extract of the plague 

 bacillus obtained by chemical reagents. For its preparation three or four day 

 agar cultures of the organism are thoroughly shaken with 1 per cent caustic 

 potash solution. 



After two hours, a 0.5 per cent acetic acid solution is slowly added until the 

 mixture becomes slightly acid, when a flocculent precipitate forms. This sedi- 

 ment is collected on filter paper, washed to a neutral reaction and finally dried 

 in vacuo. The powder when it is to be used is dissolved in 1 per cent sodium 

 carbonate solution. The dose for man is from 2 to 3 milligrams. The Swiss 

 serum institute in Bern recommends this prophylactic particularly because of 

 the fact that an exact dose can be obtained and on account of the ease with 

 which it can be transported. 



Another protective against plague has been recommended by Terni and Bandi 11 

 in 1900. For the preparation of this prophylactic guinea pigs or rabbits are 

 inoculated intraperitoneally with a small quantity of a suspension of the pest 

 bacillus in bouillon. The animal usually dies in from thirty-six to forty-eight 

 hours. At the time of its death, or a little before (in order to be sure that no 

 migration into the peritoneal cavity of the intestinal bacteria has taken place) 

 the abdominal cavity is opened, the peritoneal exudate collected and, if it is very 

 thick, diluted with saline solution. The exudate is then placed in the incubator 

 at 37° C. for twelve hours; it is next heated at from 50° to 52° C. for one hour 

 on two successive clays; in this way it becomes sterilized and the serum albumins 

 present are not coagulated. A mixture of carbolic acid, 0.5 per cent, sodium 

 carbonate 0.25 per cent, and sodium chloride 0.75 per cent is then added, in 

 order to aid in the preservation and in the absorbability of the prophylactic when 

 used. From 1.5 to 2.5 cubic centimeters are recommended for human injections. 



The method of inoculation against plague recommended by Shiga 12 is as 

 follows: The growth from a three-day agar culture which contained about 3 oesen 

 of plague organisms was placed in a mortar with 3 cubic centimeters of salt 

 solution and thoroughly rubbed up. The suspension was then heated for 30 

 minutes at 60° C. and later, carbolic acid to 0.5 per cent was mixed with 

 it. After twenty-four hours an equal volume of a pest immune serum was 

 added. Shiga recommended two injections; for the first one, 0.6 to 1 cubic 

 centimeter of the mixture of serum and organisms and for the second, after the 



Ztschr. f. Hyg. u. Infectionskrankh., Leipz. (1901), 3 6, 396. 



10 Deutsche med. Wchnsch. (1897), 23, 227, 289. 



11 Deutsche med. Wchnsch. (1900), 26, 463; also Rev. d. Hyg. Paris (1900), 

 22, 62. 



12 Ber. fiber die Pest in Kobe und Osaka, Tokyo (1900), 54. 



