The Avenues of Infection 69 



whether the inhalation of tubercle bacilli is as frequent a 

 mode of conveying that organism into the body as was once 

 supposed, it cannot be denied that its inhalation will account 

 for the far greater frequency with which tuberculosis affects 

 the lungs than other organs of the body. 



Pneumonia, caused in an immense majority of cases by 

 the pneumococcus of Fraenkel and Weichselbaum, probably 

 results from the entrance of the organism into the respira- 

 tory tissues directly. 



The entrance of the unknown infectious agents causing 

 measles, German measles, smallpox, and scarlatina, can best 

 be accounted for by supposing that they are inhaled into 

 the lungs and thus enter the blood. 



The genital apparatus is the portal of entry of micro- 

 organisms whose early or chief operations are local. Among 

 these are the gonococcus, which causes urethritis, vaginitis, 

 balanitis, posthitis, endometritis, orchitis, salpingitis, vesicu- 

 litis, cystitis, oophoritis, sometimes peritonitis, and rarely 

 endocarditis; the bacillus of Ducrey, that causes the chan- 

 croid or soft sore; and the spirochaete of syphilis. In more 

 rare cases other organisms, such as the common cocci of 

 suppuration and the tubercle bacillus, may also be trans- 

 mitted from individual to individual by sexual contact. 



The placenta usually forms a barrier through which 

 infectious agents find their way with difficulty. A study 

 of this subject by Neelow* shows that the non-pathogenic 

 organisms do not pass from the mother through the placenta 

 to the fetus. Some pathogenic micro-organisms, however, 

 readily pass through, and a few diseases, such as syphilis, 

 are well known in the congenital form. Pregnant women 

 suffering from smallpox may be delivered of infants with 

 marks indicative of prenatal disease. Some common 

 infectious agents, such as the tubercle bacillus, seem to infect 

 unborn animals with difficulty. The frequency of antenatal 

 tuberculous infection is, however, somewhat controversial 

 at present, Baumgarten having reached the opinion, exactly 

 the opposite of what is commonly believed, that most children 

 are subject to antenatal infection, though the bacilli sub- 

 sequently develop and cause disease in only a few of them. 



* "Centralbl. f. Bakt.," etc., I. abt. Bd. xxxi, Orig., Aug., 1902, p. 691. 



