THE RELATION OF BACTERIA TO DISEASE 49 



Most germs, for some obscure reason, affect by prefer- 

 ence certain parts of the body. The typhoid bacillus 

 usually lodges in the wall of the small intestine; the 

 meningococcus prefers the lining of the brain and spinal 

 cord; the gonococcus is very prone to attack the mucous 

 membrane lining the genital organs, and also the con- 

 junctival membrane (outer hning of the eye). The 

 pneumococcus affects chiefly the respiratory organs; 

 the diphtheria bacillus, the throat and nasal passages. 



The extent and kind of disease produced by the same 

 bacterium also varies greatly. This, of course, depends 

 largely on the size of the dose introduced, but also 

 on the degree of resistance of the patient. We shall 

 speak of this in a moment. 



The more important pathogenic bacteria are the 

 bacillus of tuberculosis, the typhoid bacillus, diphtheria 

 bacillus, dysentery bacillus, spirillum of cholera, the 

 pneumococcus, the streptococcus, the staphylococcus 

 pyogenes, the meningococcus, the gonococcus, the bacil- 

 lus of tetanus, of anthrax, of glanders, of bubonic 

 plague, and of malignant edema. The germs of malaria, 

 syphiHs, and sleeping-sickness are tiny organisms called 

 protozoa.! The germs of ringworm and of barbers' itch 

 are fungi. ^ The germs of smallpox, chiokenpox, scarlet 

 fever,2 measles, yellow fever, and hydrophobia have not 

 yet been discovered, though there is no doubt whate\'er 

 of the germ nature of these diseases. Several alleged 

 "cancer germs" have been described, but not only has 

 their relation to cancer not yet been proved, but there 

 is still considerable doubt whether cancer is a germ 



1 See Definitions, page 13. 

 . 2 gee page 122. 



