178 RELATIONS OF BACTERIA TO DISEASE 



In increasing the susceptibility of a given individual, con- 

 ditions of local or general diminished vitality play the most 

 important part. It has been experimentally proved that 

 conditions such as exposure to cold, fatigue, starvation, etc., 

 all diminish the natural resistance to bacterial infection. Rats 

 naturally immune to glanders can be rendered susceptible by 

 being fed with phloridzin, which produces a sort of diabetes, 

 a large amount of sugar being excreted in the urine (Leo). 

 Guinea-pigs may resist subcutaneous injection of a certain dose 

 of the typhoid bacillus, but if at the same time a sterilised 

 culture of the bacillus coli be injected into the peritoneum, they 

 quickly die of a general infection. Also a local susceptibility 

 may be produced by injuring or diminishing the vitality of a 

 part. If, for example, previous to an intravenous injection of 

 staphylococci, the aortic cusps of a rabbit be injured, the 

 organisms may settle there and set up an ulcerative endocarditis ; 

 or if a bone be injured, they may produce suppuration at the 

 part, whereas in ordinary circumstances these lesions would not 

 take place. 



Such facts, established by experiment (and many others 

 might be given), illustrate the important part which local or 

 general conditions of diminished vitality may play in the pro- 

 duction of disease in the human subject. This has long been 

 known by clinical observation. In normal conditions the blood 

 and tissues of the body, with the exception of the skin and 

 certain of the mucous surfaces, are bacterium-free, and if a few 

 organisms gain entrance, they are destroyed. But if the vitality 

 becomes lowered, their entrance becomes easier and the possibility 

 of their multiplying and producing disease greatly increased. 

 In this way the favouring part played by fatigue, cold, etc., 

 in the production of diseases of which the direct cause is a 

 bacterium, may be understood. It is important to keep in view 

 in this connection that many of the inflammation-producing 

 and pyogenic organisms .are normally present on the skin and 

 various mucous surfaces. The action of a certain organism 

 may devitalise the tissues to such an extent as to pave the 

 way for the entrance of other bacteria ; we may mention the 

 liability of the occurrence of pneumonia, erysipelas, and various 

 suppurative conditions in the course of or following infective 

 fevers. In some cases the specific organism may produce lesions 

 through which the other organisms gain entrance, e.g. in typhoid, 

 diphtheria, etc. A notable example of diminished resistance to 

 bacterial infection is seen in the case of diabetes ; tuberculosis 

 and infection with pyogenic organisms are prone to occur in 



