The Cardinal Conditions of Infection 77 



agar containing ascitic fluid, until one hundred thousand 

 millionth of a cubic centimeter (un cent milliardieme) was 

 fatal for a rabbit. In this quantity it is scarcely probable 

 that more than a single coccus could have been present. 

 Single anthrax or glanders bacilli may infect rabbits and 

 guinea-pigs. Roger found that 820 tubercle bacilli from the 

 culture with which he experimented were required to infect 

 a guinea-pig, when introduced beneath the skin. Herman 

 found that it required 4 or 5 c.c. of a culture of Staphylococ- 

 cus pyogenes to produce suppuration in the peritoneal cavity 

 of an animal; 0.75 c.c. to produce it beneath the skin; 0.25 

 c.c. in the pleura; 0.05 c.c. in the veins and o.oooi c.c. in the 

 anterior chamber of the eye. 



In experimenting with Bacillus proteus vulgaris, Watson 

 Cheyne found that 5,000,000 to 6,000,000 organisms injected 

 beneath the skin did not produce any lesion ; 8,000,000 caused 

 the formation of an abscess; 56,000,000 produced a phleg- 

 mon from which the animal died in five or six weeks and 

 225,000,000 were required to cause the death of the animal 

 in twenty-four hours. In studying Staphylococcus aureus 

 upon rabbits he found that 25,000,000 would cause an 

 abscess, but 1,000,000,000 were necessary to cause death. 



3. The Avenue of Infection. The successful invasion 

 of the body by certain bacteria can be achieved only when 

 they enter it through appropriate avenues. Even when 

 invasion is possible through several channels, it is usually 

 found that one of them, that by which the parasite most 

 commonly invades the host, is most appropriate, and that 

 invasion through it furnishes the typical picture of the 

 infection. 



Thus, gonococci usually reach the body through the uro- 

 genital mucous membranes, where they set up the various 

 inflammatory reactions collectively known as gonorrhea 

 i. e., urethritis, vaginitis, prostatitis, orchitis, cystitis, etc. 

 These constitute the typical picture of infection. The 

 organism may also successfully invade the conjunctiva, 

 producing blennorrhea, but there is no evidence that gono- 

 cocci can successfully invade the body through the skin or 

 alimentary mucous membrane. 



Typhoid and cholera infections seem to take place through 

 the alimentary mucous membrane, and the evidence that 

 infection takes place by inhalation is slight. It is not known 

 to take place through the urogenital system, the conjunctiva, 

 or the skin. 



