618 STAPHYLOCOCCUS 



which may inhibit the clotting of the plasma. Other sources of error have been pointed 

 out by GUlespie (1943). According to Duncan and Walker (1942), the result of the test 

 is influenced by the proportion of culture to plasma in the mixture. The optimal pro- 

 portion can be determined in the usual way by titrating a series of increasing dilutions 

 of culture against a fixed volume of plasma, or of increasing dilutions of plasma against 

 a fixed volume of culture. Tests for the presence of coagulase may also be made by the 

 slide method (Cadness-Graves et. al. 1943). 



Though there is a high correlation between coagulase and a-hsemolysin produc- 

 tion, there seems little doubt that these two substances are distinct. The hsemo- 

 lysin is destroyed in half an hour by exposure to a temperature of 56° C, whereas 

 the coagulase is not (Vanbreuseghem 1934, Cruickshank 1937, Smith and Hale 

 1944). The hsemolysin is absorbed by red corpuscles, the coagulase is not. An 

 antibody to the haemolysin can readily be obtained by the inoculation of rabbits, 

 but not to the coagulase (Gross 1931a). Coagulase is formed almost exclusively 

 by strains of Staph, aureus or by albus variants of aureus strains. Cruickshank 

 (1937) maintains that coagulase production constitutes the most convenient and 

 reliable single test for estimating the pathogenicity of a given strain. This con- 

 tention is supported by a number of subsequent workers (Chapman et al. 1938, 

 Marcuccio 1938, Gillespie, Devenish and Cowan 1939, Fairbrother 1940, Christie 

 and Keogh 1940). 



The method of coagulase action is not yet clearly understood. According to 

 Smith and Hale (1944) coagulase itself is a thermostable substance, filtrable 

 through a gradocol membrane having an A.P.D. of 0-31 m/^, but completely held 

 back by one of 11 m/{. It appears to be the precursor of a thermolabile thrombin- 

 like substance, the production of which depends on the participation of an activator 

 present in the plasma of some animals, but deficient or lacking in others. The 

 staphylocoagulase reaction resembles normal thrombin formation from prothrombin 

 under the influence of thrombokinase except that calcium is not required. 



Pathogenicity. — The staphylococci can be fairly sharply divided into patho- 

 genic and non- pathogenic types. Thus the great majority of strains isolated from 

 suppurative lesions in the animal body are found to be pathogenic for rabbits, 

 and to a less extent for mice and guinea-pigs. On the other hand, the great 

 majority of strains isolated from normal skin, air, water, dust, etc., are harmless 

 to these animals. Sometimes the virulence of the pathogenic strains diminishes 

 on prolonged cultivation, but this is not always so ; even after years of sub- 

 culture in the laboratory the virulence may remain intact. Moreover, by passage 

 through rabbits, it is generally possible to raise the virulence of a strain which 

 has become temporarily avirulent ; with the saprophytic strains this is impossible. 

 According to Lubinski (1894) the virulence of Staph, aureus for rabbits can be 

 increased by growth under anaerobic conditions ; growth in pure oxygen was 

 said to have the reverse efiect. 



Man. — The staphylococci which are responsible for disease in the human body 

 generally belong to the aureus or albus varieties ; only occasionally can Staphylo- 

 coccus citreus be incriminated. Staphylococcus aureus is more pathogenic to man 

 than Staphijlococcus albus ; it gives rise to the severer lesions, such as osteomyelitis, 

 pyaemia — sometimes associated with an infective endocarditis — mastitis, boils and 

 abscesses in various parts of the body, and on occasion to a peculiarly fatal form 

 of broncho-pneumonia (Finland, Peterson and Strauss 1942), whereas Staphylococcus 



