PRINCIPLES OF BACTERIOLOGY 



bacterial or other, acute and chronic diseases, vicious habits, drunken- 

 ness, etc. Purely local injuries, such as wounds, contusions, etc.., give 

 a point of entrance for infection, and a point of less resistance, where 

 the bacteria may develop and produce local inflammation. Local 

 affections, such as endocarditis, may also afford an area of lessened 

 resistance for the bacteria to seize upon. The presence of foreign 

 bodies in the tissues in like manner predisposes them to bacterial 

 invasion. Interference with free circulation of blood and retention in 

 the body of poisonous substances which should be eliminated also tend 

 to lessen the vitality. In these and other similar ways animals which 

 are otherwise refractory may acquire a susceptibility to disease. 



Increase of Resistance by Non-specific Means. Just as all conditions 

 which are deleterious to the body lessen its power of resistance to 

 bacterial invasion, so all conditions which are favorable to it increase, 

 its resistance, and thus aid in preventing and overcoming infection. 

 The internal use of antiseptics against bacteria has not proved success- 

 ful, for the reason that an amount too small to inhibit bacterial growth 

 is found to be poisonous to the tissue cells. The efficacy of quinine in 

 malaria and mercury in syphilis is, possibly, an exception to the rule, 

 but in both cases we are dealing probably with animal parasites, not 

 with true bacteria. Such substances as nuclein and others contained 

 in blood serum, when introduced into the body in considerable quan- 

 tity, aid somewhat in inhibiting or preventing the growth of many 

 bacteria. Even bouillon, salt solution, and small amounts of urine 

 have a slight inhibitory action. The hastening of elimination of the 

 bacterial poisons by free intestinal evacuation and encouragement of 

 the functions of the skin and kidneys are also of some avail. The 

 enzymes formed by certain bacteria have been found to exert a slight 

 bactericidal action not only on the germs which have directly or indi- 

 rectly produced them in the body, but also on other varieties. None 

 of these enzymes are sufficiently protective to be of practical value nor 

 equal in power to the protective substances formed by the tissues from 

 the bacterial products. 



Use of Local Treatment in Limiting Bacterial Invasion. The total 

 extirpation . of the infected area by surgical means, if thoroughly 

 carried out, removes the bacteria entirely; but, unfortunately, this pro- 

 cedure is rarely possible. When incomplete it is frequently helpful; 

 but it may be harmful, for by creating tissue injury and exposing fresh 

 wounded surfaces to infecion it may lead to the further development of 

 the disease. Again, it is usually insufficient, for by removing only a 

 portion of the bacteria it may leave those which have already reached 

 the deeper tissues or blood to go on developing. In some cases, like 

 anthrax and infection from bites of rabid animals, total or almost com- 

 plete removal of the virus is possible, either by the knife or thorough 

 cauterization, and will prevent a general infection or so lessen the num- 

 ber of bacteria in the body as to allow the bactericidal elements of its 

 fluids to exterminate them. So also in tetanus, the invasion being 

 limited, surgical interference may be of great use by removing not only 



