INFECTION. 45 



by exposure to cold, in pigeons by hunger or long-con- 

 tinued withholding of water, and in white mice to glanders 

 by the production of phloridzin-diabetes. In the same way, 

 intoxication with alcohol or with various substances, espe- 

 cially such as are destructive of the blood-corpuscles, gives 

 rise, temporarily, to especial susceptibility. The predispo- 

 sition of diabetics to certain infections (suppuration, gan- 

 grene, tuberculosis) may also be mentioned. Likewise, a 

 temporary predisposition is established, according to the 

 well-known theory of Pettenkofer, through telluric (ground- 

 water elevation) and temporal influences (summer's heat) 

 when an epidemic of cholera occurs. 



In addition to the general predisposition a local predis- 

 position may be distinguished, depending upon the varying 

 susceptibility of the different tissues of the body. Her- 

 mann undertook the establishment of a scale of susceptibility 

 for the staphylococcus. The anterior chamber of the' eye 

 proved most susceptible ; then followed the circulatory 

 apparatus of the rabbit ; next the subcutaneous connective 

 tissue of the dog ; then the pleura, the cerebral meninges, 

 the subcutaneous tissue, and the peritoneum again of 

 the rabbit. Little is known with regard to the actual con- 

 ditions upon which the degree of predisposition or suscep- 

 tibility of a body for a given species of bacteria is depend- 

 ent. The word predisposition is only an expression for 

 the sum of resistances that the body offers to infection. 

 What the nature of these resistances is will be fully dis- 

 cussed in the next section in a consideration of the subject 

 of immunity. 



A certain measure of resistive influences against infection 

 must be present in every animal tissue ; at least, there ap- 

 pears to be no absolute susceptibility. The weapons of 

 the bacteria against these resistances are most probably 

 their toxins ; in this way the significance of the virulence 

 and of the amount of the infectious agents introduced is 

 rendered comprehensible. On the other hand, it must be 

 assumed that the devices mentioned that are capable of in- 

 creasing the susceptibility (inanition, overexertion, over- 

 cooling and overheating, anemia, glycemia, etc.) diminish 

 these resistances of the organism. 



With regard to the susceptibility of human beings to bac- 

 terial diseases, this is comparatively slight for most infec- 

 tious diseases for the suppurations, pneumonia, cholera, 



