FACTS AND PROBLEMS OF IMMUNITY 307 



following phenomena can be regularly observed: Minimal doses of the 

 culture produce a febrile condition which continues for a few hours with 

 no serious symptoms. Slightly larger doses give rise, after a short 

 interval, during which there is fever, to a marked drop in tempera- 

 ture and definite symptoms of cholera poisoning muscular weakness, 

 twitching, and general prostration. These symptoms of poisoning then 

 gradually disappear, and after twenty-four hours the guinea-pigs are 

 again normal. If the quantity of cholera culture injected is carefully 

 increased up to the minimal lethal dose, the animal dies with all the 

 symptoms of cholera intoxication, but on autopsy the peritoneum is 

 found to be entirely sterile, or only a few isolated cholera spirilla are 

 found, usually inclosed in pus cells. Finally, if larger quantities of 

 living cholera spirilla are injected, the peritoneal cavity shows a profuse, 

 serous, sometimes hemorrhagic exudate, which contains innumerable 

 actively motile microorganisms. The point of interest in this experi- 

 ment is the demonstration of the fact that the normal guinea-pigs 

 which receive enough of the cholera vibrios to prove fatal have de- 

 stroyed the vibrios and presumably died from the poison thus liberated, 

 and not from poisons secreted by living vibrios, or from an overcoming 

 of their systems by the rapid multiplication of the organisms. It is only 

 when the animal system is previously flooded with an overwhelming dose 

 that the vibrios are found alive and multiplying even locally in the peri- 

 toneum after death. This does not mean, however, that no multiplica- 

 cation ever goes on hand in hand with the destruction of the germs in the 

 infected animal ; on the contrary, such a multiplication is probably the 

 rule rather than the exception, as has been shown fairly conclusively 

 by the experiments of Radziewsky, and was beautifully illustrated by 

 an experiment of Pfeiffer and Wassermann, who after having shown that 

 the blood serum of human beings who have recovered from Asiatic chol- 

 era has the power to protect guinea-pigs from ordinarily fatal doses 

 of cholera spirilla, even when used in high dilutions, then proved that 

 this protective power is not an antitoxic one, but depends largely, if 

 not entirely, on the ability of the serum to aid in the immediate dissolu- 

 tion of the vibrios. Thus animals which received only a fraction of a 

 milligram of such a serum were able to bear the injection of a loopful of 

 virulent cholera vibrios, practically without reaction, while control 

 animals succumbed to one-fourth of the dose with typical symptoms. 

 Now, however, if the dose was increased to three or five loopfuls, not 

 even ten thousand times the original amount of the serum would protect 

 the animals against the inoculation. The toxic effects may, in fact, as 



