6 MEDICAL BACTERIOLOGY 



Arthrospore formation has been described by some authorities and denied 

 by others. 



Occasionally a culture of cocci especially staphylococci is found which is 

 much more resistant to the germicidal action of heat, chemicals, etc., than the 

 average, the resistance at times being so great as to suggest the presence of 

 spores. Stained preparations from such resistant cultures frequently show some 

 organisms which differ from the majority of their fellows in size; they are 50 

 to 100 per cent, larger than normal; some of them slain normally and others 

 are resistant to staining. These bodies are considered to be spores (arthro- 

 spores) by some. 



There are a few bacteria that thrive at oC. (psychrophilic) and others that 

 flourish at temperatures above 7oC., (thermophilic) but the majority develop 

 most luxuriantly at or near the temperature of the human body. Generally, 

 warmth, moisture and protection from direct sun rays, are required for bacterial 

 development. 



Among both saprophytic and pathogenic bacteria, there are species which 

 flourish in an atmosphere containing oxygen, as air, and die or change into spores 

 when placed in an atmosphere devoid of oxygen these are called obligate 

 aerobic bacteria. There are obligate anaerobic bacteria which thrive only in 

 an atmosphere free from oxygen and do not propagate when exposed to air. 



Some bacteria grow best in air, but can grow to a lesser degree in the absence 

 of air or oxygen these are called aerobic and facultative anaerobic. There are 

 bacteria, however, which are anaerobic and facultative aerobic, and some that 

 grow equally well, whether in an aerobic or anaerobic environment. 



The life of bacilli is very variable and is influenced by environment; in this 

 respect different species show marked variations. 



In a resting, inactive, or dormant state, some species survive for months or 

 years. In full, continuous activity, the life of a single organism is a matter of 

 minutes, from 1 6 to 20 minutes for the bacillus coli communis. 



According to A. Fischer, under ideal conditions, 1,600,000,000,000,000 ba- 

 cilli would develop from a single organism in 24 hours. Of course, ideal con- 

 ditions for propagation never exist and increase is always much less than the 

 potential reproductive power of any organism. 



Just as for the individual, there is a limit to the growth and life of colonies of 

 bacteria, dependent upon available food, environment and an inherent tend- 

 ency to involute and die in the course of time. 



Most bacteria are saprophytic. They live on dead animal and vegetable 

 matter and by their activity, rapidly change its character, splitting it into simpler 

 compounds, liberating water, carbonic acid, ammonia and ptomains. Sapro- 

 phytic bacteria, with a few exceptions, are unable to survive in living animal 

 bodies and cannot directly cause disease. Indirectly they are capable of harm. 

 Lodged upon the dead cells covering the surface of the body of a living animal, 

 feeding upon these dead cells and splitting them into simpler compounds, some 

 of which are irritant or toxic to adjacent living cells, they injure and impair 

 the function of the living cells and enhance the possibility of entrance at that 

 point of pathogenic bacteria. 



