44 BIOLOGY OF BACTERIA 



Staphyloccus pyogenes aureus and the influenza bacillus; the diph- 

 theria bacillus and the streptococcus. On the other hand, two dif- 

 ferent species of bacteria when growing together may show a mutual 

 antagonism and a retarding influence. Such antagonism exists 

 between the anthrax bacillus and the Staphylococcus pyogenes aureus, 

 the anthrax and typhoid bacilli. Other bacilli ma} not show any 

 influence at all upon each other's growth as the typhoid and colon 

 bacilli or as the cholera spirillum and certain non-pathogenic water 

 spirilla. When symbiotic bacteria invade man or domestic animals 

 simultaneously or nearly so, they are liable to produce a very virulent 

 form of mixed infection. This has been observed in man in diphtheria 

 with simultaneous streptococcus infection of the tonsils. 



Influences Inimical to Bacterial Growth and Life. We have 

 already seen that bacteria for their metabolism, growth, and multi- 

 plication require certain definite conditions of the nutritive material, 

 its concentration, moisture, reaction, the prevalence of a certain 

 temperature, and the presence or absence of oxygen. It has also 

 been shown that any excess of alkalinity or acidity is very detri- 

 mental, and that particularly mineral acids, even in very moderate 

 concentration, speedily kill pathogenic bacteria. It has also been 

 explained how their own accumulating metabolic products bring 

 about the same result. In addition, the following outside inimical 

 influences may be mentioned briefly. 



Sunlight. Many bacteria can stand the sunlight quite well; others, 

 particularly pathogenic bacteria, are rapidly killed by such exposure; 

 with them even diffuse daylight, when acting long enough, frequently 

 proves fatal. 



Electricity. Electricity passing through a fluid culture medium 

 forms acids and alkalies which are very detrimental to bacteria; 

 ic-rays, as far as known, have no effect. 



Chemicals. Some chemicals, such as corrosive sublimate, chloride 

 of lime, permanganate of potash, carbolic acid, creosote, creolin, 

 lysol, formalin, etc., even in weak concentration, have a tendency 

 to kill bacteria rapidly. Chemicals which possess this property are 

 called antiseptics or germicides. 



Heat. Heat, particularly when moist, is very inimical to micro- 

 organisms. As a rule, most disease-producing bacteria in the vege- 

 tative form are killed by a short exposure (ten minutes) to a com- 

 paratively moderate temperature (say 55 to 60 C.). This heat, how- 

 ever, must be moist; if dry and the bacteria are in the same condition 

 they can often stand much higher temperatures and longer expos- 

 ures. Spores, however, can often stand a long exposure to moist 

 heat at high temperatures (100 C.). When instruments, sutures, and 

 bandaging material are exposed to the heat of boiling water or steam 

 at 100 C., it is done with the object of killing all bacteria and their 

 spores. Such a procedure, provided it has been done successfully, 

 is called sterilization. 



