ANAEROBIC ORGANISMS 501 



anaerobes are manifold and may broadly be divided into attack 

 on carbohydrates and decomposition of proteins. In the fer- 

 mentation of carbohydrates acetone, alcohols, particularly butyl 

 alcohol, and volatile fatty acids, particularly butyric acid, are 

 formed. Non-volatile fatty acids, particularly lactic acid, may 

 also be formed in quantity. Practically all the anaerobes exert 

 a certain amount of tryptic action and break down proteins to 

 amino acids and ammonia, though the amount of this digestion 

 by some anaerobes may be slight and inappreciable. Proteoses 

 and peptones may also be formed together with sulphuretted 

 hydrogen and mercaptans. Carbon dioxide is frequently pro- 

 duced in quantity, but is derived from a carboxyl group by simple 

 elimination after breaking down of a carbon chain, and not by 

 combustion of the carbon atom as is the case with aerobes. 



It is a common feature of the pathogenic anaerobes that when 

 the washed organisms, free from admixture with other substances, 

 are injected into a susceptible animal, no pathogenic effect follows, 

 except, perhaps, some local oedema and necrosis which may result 

 in an abscess. On the other hand, unwashed organisms contain- 

 ing traces of adherent toxin produce infection. Other substances 

 also have a similar effect, notably ionizable calcium salts, such as 

 calcium chloride, and colloids, such as silicic acid and gelatin. It 

 is probable that in naturally occurring anaerobic infections of 

 dirty wounds, the soluble calcium salts of the soil contaminating 

 the wound may be of paramount importance in the genesis of the 

 infection, for it is improbable that the organisms or their spores in 

 the soil have a sufficiency of adherent toxin to induce infection. 



The study of anaerobic organisms is beset with pitfalls and 

 difficulties their cultural characters are not well defined, and are 

 less distinctive than those of many other organisms, their staining 

 reactions are liable to vary according as they are under natural 

 or artificial conditions of growth, the pathogenicity of different 

 strains of the same organism varies enormously, the same organism 

 has sometimes been described under a number of synonyms, and 

 lastly extreme difficulty may be experienced in obtaining pure 

 cultivations. Thus cultures which for months appear to be pure 

 ones, and continuously give the same appearances and reactions, 

 may ultimately be found to consist of two distinct species. 



Ordinary media may be employed for the culture of many 

 anaerobes, glucose agar is particularly useful, and blood-broth, 



