88 Infection 



ever able to cause infection because of the uncertainty of its being 

 able to withstand the changed conditions to which it is subjected. 

 In most cases a considerable number of organisms is necessary in 

 order that some may survive. Park points out that when bacteria 

 are transplanted from culture to culture, under conditions supposed 

 to be favorable, many of them die. It seems hot improbable, there- 

 fore, that when they are transplanted to an environment in which are 

 present certain mechanisms for defending the organism agaifist them, 

 many more must inevitably die. The more virulent an organism 

 is, the fewer will be the number required to infect. Marmorek, 

 in his experiments with antistreptococcic serum, used a streptococcus 

 whose virulence was exalted by passage through rabbits and in- 

 termediate cultivation upon agar-agar containing ascitic fluid, until 

 one hundred thousand millionth of a cubic centimeter {un cent 

 ynilUardieme) 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 ce. of a culture of Staphylococcus pyogenes to produce suppura- 

 tion in the peritoneal cavity of an animal; 0.75 cc. to produce it 

 beneath the skin; 0.25 cc. in the pleura; 0.05 cc. in the veins and 

 o.oooi cc. 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 phlegmon 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. 



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, the parasite most commonly invades through one 

 that may, therefore, be regarded as most appropriate, and furnishes 

 the typical picture of the infections. 



Thus, gonococci usually reach the body through the urogenital 

 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 the infection. The organism may also successfully invade 

 the conjunctiva, producing blennorrhea, but there is no evidence 

 that gonococci can successfully invade the body through the skin, 

 the respiratory, or alimentary mucous membranes. 



