ANTIBIOTICS 157 



aljle to another which then dies out. We are concerned 

 here only with bacteriostatic or bactericidal substances 

 produced by micro-organisms. vSoil is a rich source of 

 micro-organisms which have antibiotic properties. 



A considerable number of antibiotic substances is 

 now known. The more important of them will be dealt 

 with in turn. 



Actinomycetin. — Many species of Actinomycetes pro- 

 duce substances which are lytic to living and dead 

 bacteria. Thus Actinomyces alhus yields the water 

 soluble, thermolabile protein-like material actinomj^cetin 

 which will lyse living or dead Gram -positive organisms 

 and dead Gram -negative organisms. It can be precipi- 

 tated by alcohol and appears to have the properties of a 

 proteolytic enzyme. A similar substance has been 

 isolated from A. violaceus, which, although heat stable, 

 otherwise resembles the enzyme lysozyme w^hich occurs 

 in egg white and tears and lyses most non-pathogenic 

 bacteria and also streptococci and staphylococci. Its 

 substrate is a mucopolysaccharide which it breaks down 

 to an acetylated amino -he xose and a ketohexose. 



Actinomycin. — The brown pigmented soil organism 

 A. antihioticus is very active against almost all bacteria, 

 and fungi, especially Gram -positive bacteria. An active 

 substance, actinomycin, was isolated from it by extraction 

 with ether and fractionated into actinomycin A, soluble 

 in alcohol and in petrol and giving a clear aqueous 

 solution, and actinomycin B which is soluble in petrol, 

 difficultly soluble in alcohol and gives a turbid suspensino 

 in water. 



Actinomycin A is a bright red crystalline polycyclic 

 nitrogen compound, C, 59-0 per cent. ; H, 6-68 per 

 cent. ; N, 13-35 per cent. ; m.p. 250°C. (with decomposi- 

 tion), [a]u^ — 320° It has a molecular weight about 80 0. 

 It hgis the properties of a reversible oxidation-reduction 

 indicator and is probably of quinoid structure. It is 



