GENERAL FEATURES OF BACTERIA 163 



Facultative saprophytes ordinarily live in living tissues, but can 

 with difficulty be cultivated outside, e.g., gonococci. 



Conditions necessary for bacterial existence or activity. 



Proteid food in an assimilable form. Water. Temperature at or 

 about blood heat. Darkness. Oxygen or its absence. 



Aerobes, e.g., pyogenic cocci, require oxygen. 



Anaerobes, e.g., B. tetani, cannot live in oxygen. But they can 

 often live in company with other bacteria which absorb oxygen even in 

 the presence of air; e.g., B. tetani can grow in a surface wound if it is 

 contaminated by cocci. 



Conditions causing a suspension of bacterial activity or groivth. 



Absence of pabulum. Dryness. Cold. Sunlight. 



Conditions causing bacterial death. 



Heat at or below boiling pomt quickly kills all except spores. 



Spores require temperature of 25o°F. or long boiling to kill. 



Chemical reagents, e.g., carbolic acid, mercury salts, etc., must be 

 of a certain strength ; act for a certain time and come into intimate 

 contact. 



In all conditions in which the living tissues are more potent than 

 the bacteria. 



Products of bacterial activity ivhe7i growing in living tissues. 



Acids or alkalies, e.g., B. coli produces an acid. 



Gases (rare), e.g., B. coli and B. oedematis maligni. 



Pigments (rare), e.g., B. pyocyaneus. 



Aromatics. Indol, phenol. Alcohols. 



Ferments. Diastase, curdling ferment, proteolytic ferment. 



Ptomaines. Crystallizable alkaloids. 



Toxins. The specific poisons, probably albumoses. 



(a) Intracellular toxins, e.g., tuberculosis. The toxin remains 

 closely associated with the bacillus, and only acts in its 

 neighbourhood. 



(b) Extracellular toxins, e.g., diphtheria, tetanus. 



The toxin is found in the bodv fluids, and acts at a distance from 

 the bacteria. 



THEORIES OF IMMUNITY. 



The tissues acquire two methods of defence. 



(i) They kill the bacteria; antibacterial action. 



(2) They neutralize the toxins; antitoxic action. 



Antitoxic action is an actual chemical antithesis to the toxin 

 produced in the blood bv infection. 



lliis is a proteid, and is called antitoxin : it can be made to 

 neutralize the toxin outside the body. 



Best exemplified in diphtheria and tetanus. 



