68 Infection 



litis, cystitis, oophoritis, sometimes peritonitis and rarely 

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

 croid or soft sore ; and the micro-organism of syphilis, what- 

 ever it may be. In more rare cases other organisms, such 

 as the common cocci of suppuration and the tubercle bacillus, 

 may also be transmitted from individual to individual by 

 sexual contact. 



The placenta usually forms a barrier through which 

 infectious agents find their way with difficulty. Some 

 micro-organisms, however, readily pass through, and a few 

 diseases such as syphilis are well known in the hereditary, 

 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 com- 

 monly believed, that most children are subject to antenatal 

 infection, though the bacilli subsequently develop and cause 

 disease in only a few of them. 



MODES OF BACTERIAL PATHOGENESIS. 



This subject can be understood only through a broad 

 knowledge of the metabolic products of the bacteria. In 

 general it may be said that the ability of micro-organisms 

 to do harm depends upon the injurious nature of their 

 products. This alone, however, will not explain the pheno- 

 mena of infection, for in many cases the intoxication is 

 subsidiary in importance to the invasive power of the micro- 

 organisms. Some bacteria having but limited toxic powers, 

 possess extraordinary powers of invasion, as B. anthracis, 

 and the intoxication becomes important only after the 

 organisms have penetrated to all the tissues of the body. 

 Others, with more active toxic properties, have but limited 

 invasive powers, and a few organisms, growing with diffi- 

 culty in some insignificant focus, excite actively destructive 

 reactions in the tissues with which they come into contact. 

 Still others, with limited invasive powers, eliminate active 

 toxic substances, soluble in nature, that enter the circulation 

 and act upon cells remote from the bacteria themselves, as 

 in diphtheria and tetanus. 



The invasive power of the bacteria depends upon their 



