BIOLOGICAL CONDITIONS 1 7 



various phosphates. Intracellular toxins in combination with 

 the cytoplasm are found in certain groups of bacteria, e.g., B. 

 typhosus. y{ 



BIOLOGICAL CONDITIONS. 



y( Bacteria are arbitrarily classed either as Parasites, or saprophytes^ 

 They may be so dependent upon the tissues of the infected organism 

 as to be a strict parasite and" incapable of growth under any other 

 conditio-nf(Mycobact. leprcz) , or they may be capable of life on arti- 

 ficial culture media (tubercle bacillus), or of life in the body, on 

 culture media, or in the soil (B. tetani). jf 



j( The bacteria of the soil, water, air, etc., that are incapable of 

 successful life in the body tissues are called saprophytes. jf 

 y( Certain biological conditions are essential for the growth of bac- 

 teria: water, oxygen, carbon, nitrogen, and salts are necessary. 

 For certain parasitic bacteria, highly complex substances are indis- 

 pensable: meat albumins, peptones, milk, egg albumin, blood 

 serum, and sugars are the ingredients of various culture media. Jf 

 X The chemical reaction of such media is important: it should either 

 be faintly acid or faintly alkaline. The greatest number of water 

 bacteria grow in media that are slightly acid, while diphtheria prq^ 

 duces its strongest toxins and grows best in alkaline media. Salt 

 free metlia is required for a number of pathogenic bacteria, e.g. 

 the Gonococcus, B. Leprse.^C 



)f All bacteria require for their growth either free oxygen, as in air, 

 or combined oxygen, as in albumin, water, etc. Those that only 

 grow when deprived of free oxygen are known as obligate anaerobes^ 

 while those that require the presence of oxygen are called obligate 

 aerobes. Those that grow under either conditions are uB.me(Tfacul- 

 tative^anaerobes. Free oxygen is needed for spore formation by cer- 

 tain bacteria. Anaerobes obtain oxygen as they need it by breaking 

 up their food stuffs. rf 



~\ Nutriment is most important for the growth of bacteria, nitrog- 

 enous compounds (albumins) particularly being required. Simple 



