620 STAPH YLOGOCOUS 



Mice and Guinea-pigs are much less susceptible than rabbits, and though death may 

 follow the intraperitoneal injection of virulent cultures, there is frequently no more than 

 a local abscess formation from which the animal recovers. 



Protection Experiments. — Proscher (1903), who attempted to prepare an immune 

 serum suitable for prophylactic and therapeutic use, obtained some hopeful results 

 by the injection of living, virulent staphylococci into goats and horses. 1-5 ml. 

 of immune goat serum given subcutaneously protected rabbits against 0-5 ml. of 

 a virulent broth culture injected intravenously 24 hours later. But if given at 

 the same time as, or subsequently to, the injection of the cocci, it had but little 

 or no effect. In spite of numerous studies by such workers as Forssman (1935-41), 

 Blair and Hallmann (1935), Kitching and Farrell (1936), Lyons (1937), Downie 

 (1937), Smith (1937), Cowan (19396), and Valentine and Butler (1939), the mechan- 

 ism of immunity in natural and experimental infections of man and animals with 

 staphylococci still remains obscure. Serum prepared by the injection of rabbits 

 or horses with toxoid, and later with toxin, has a high antitoxic titre, and may 

 save the life of test animals inoculated prophylactically ; but it seems to have 

 little or no direct bactericidal effect, so that local abscess formation is not neces- 

 sarily prevented. An international standard for staphylococcal antitoxin has now 

 been laid down ; one unit is contained in 0-2376 mgm. of the standard preparation 

 (Smith and Ipsen 1938). The potency of the serum is titrated by the hsemolytic 

 method using rabbit red corpuscles, by the intracutaneous injection of guinea-pigs, 

 and by the intravenous injection of mice. 



Classification 



Little useful purpose would be served by describing the numerous attempts 

 that have been made to provide a satisfactory classification for the staphylococci. 

 Those who are interested should consult the studies of Rosenbach (1884), Winslow 

 and Rogers (1906), Dudgeon (1908), Kligler (1913), Winslow, Rothberg and Parsons 

 (1920), Hucker (1924a), and Dudgeon and Simpson (1928). Nearly all workers 

 are agreed that there is a gradation from the actively fermentative, gelatin-lique- 

 fying, pathogenic group, of which the type is Staph, aureus, down to the weakly 

 fermentative, gelatin-non-liquefying, saprophytic group, of which Gordon's scurf 

 staphylococcus is a typical representative. No sharp line of cleavage occurs, and 

 no single property can be regarded as satisfactory as a basis for classification. 

 Though there is something to be said for dividing the staphylococci into a patho- 

 genic group. Staph, pyogenes (Cowan 1938), and a non-pathogenic group, Staph, 

 saprophyticus (Fairbrother 1940), on the basis of coagulase production, we doubt 

 whether there is much to be gained, partly because the production of golden pig- 

 ment and coagulase are fairly highly correlated, partly because coagulase production 

 has not yet been established as a certain indicator of potential pathogenicity and 

 partly because pathogenicity is not a good criterion on which to establish specific 

 differences. It is true that we recognize the name Streptococcus pyogenes, but here 

 the differentiation is based on the firmer ground of antigenic structure. Until the 

 serological study of the staphylococci has progressed further we think it best to 

 keep to the time-honoured names of Staph, aureus, Staph, albus, and Staph, citreus, 

 and taking account of more recent knowledge to define them tentatively as 

 follows : 



Staphylococcus aureus is a pathogenic species, producing suppurative lesions of 



