96 SAPROPHYTISM, PARASITISM, AND PATHOGENISM 



typhoid, dysentery and cholera organisms may be excreted in the feces 

 through long periods of time, rarely or never, however, in the urine. 

 Slowly progressing focal diseases, as pulmonary tuberculosis are, 

 in a sense, spread by carriers, for the patient may survive for years, 

 excreting daily large numbers of tubercle bacilli. The line of demarca- 

 tion, in other words, between the human bacillus carrier and the 

 patient in whom a focal disease is chronic for long periods of time is 

 not sharply circumscribed. 



7. Contact Infection. The direct transmission of bacteria from man 

 to man is well exemplified in the venereal diseases, gonorrhea and 

 syphilis, which are usually transmitted by direct contact. Diseases 

 of the respiratory tract, as tuberculosis, diphtheria and whooping- 

 cough, may be transmitted directly from patient to patient by kissing, 

 swapping chewing gum, by eating utensils, etc. Soiled fingers may 

 transmit the typhoid bacillus from a typhoid patient to other indi- 

 viduals. All of the excrementitious diseases may be spread in a 

 similar manner, under certain conditions. 



8. Germinal and Prenatal Infection. True germinal infection implies 

 that a disease-producing microorganism is carried by the ovum or 

 spermatozoa and incorporated in the embryo prior to its development. 

 This method of transmission is not definitely worked out, although it 

 has been claimed that syphilis may be thus transmitted by the male 

 to the ovum in utero, the mother remaining uninfected by the disease. 



In prenatal infections the organisms must pass the placental 

 barrier. This implies that the fetus becomes infected directly from the 

 maternal blood stream, or by continuity of growth of the organisms 

 through the placenta. The placental form of infection is not conceded 

 by all observers, but it is reasonably certain that congenital syphilis 

 may be contracted thus. Smallpox, measles, dysentery, various 

 pyogenic infections, and, rarely, pneumonia are occasionally said to be 

 prenatally transmitted to the fetus. With respect to tuberculosis, 

 there is difference of opinion. A very few cases are on record in which 

 prenatal infection seems almost certainly to have taken place, for the 

 newborn infant exhibited lesions which were so far advanced that no 

 other explanation than prenatal infection suffices to explain them. 



C. Portal of Entry; Atria of Invasion. The bacteria which cause 

 infection in the human body may be provisionally divided into two 

 great groups: those of exogenous origin, which are not habitual 

 parasites of man; and those of endogenous origin, which are habitual 

 parasites of man. 



