no THE POSSIBLE OCCURRENCE OF [ch. vm 



of these observers, on repeating the experiments of earlier 

 investigators, to obtain the same results, somewhat invalidates 

 the conclusions of the latter, so that the question of the possi- 

 bility of a mutation between the two species remains sub 

 jvdice. 



Several species of staphylococci are recognised, — S. 

 epidermidis albus, 8. pyogenes albus, 8. pyogenes aureus. 

 The distinction between these three rests on their inequality 

 in virulence, on their different powers of fermenting carbo- 

 hydrates, and, as their names imply, on their dissimilarity in 

 the production of pigment. 



.As regards virulence, the first-named organism is normally 

 present in the skin of healthy persons and is non-pathogenic ; 

 the second possesses slight virulence, producing mild local 

 inflammatory conditions ; while the third is a virulent organism 

 found in pathological conditions such as suppurative cutaneous 

 and subcutaneous lesions, acute bone infection and septicaemia. 

 8taphylococGus epidermidis albus may however assume a 

 certain degree of virulence and give rise to a stitch abscess 

 or mild inflammation (Dudgeon and Sargent, 1907) and plays 

 an important rdle in peritonitis {ibid.). Andrewes and Gordon 

 (1905-6) isolated it in pure culture in one case of otitis media 

 and also from a boil. The 8tapJiylococeus pyogenes albus can 

 be made much more virulent by artificial passage. It has been 

 known to become parasitic, invading the human body and 

 circulating in the blood stream (Panichi, 1906, Southard, 1910). 



In the second place, as regards their fermenting properties, 

 Gordon (1904-5) has shown that strains of 8taphylococeus 

 albus isolated from the skin of healthy persons show very 

 great diversity in their fermenting power. In an earlier paper 

 (1903-4) he describes two strains, one a 8taph. aUms derived 

 from the skin and the other a 8taph. pyogenes aureus derived 

 from pus — which, when "put through" no less than 20 carbo- 

 hydrate substances, revealed different fermenting power in 

 one only, namely mannite. 



In the third place, as regards pigment formation, it has 

 been proved by many investigators (Neumann, Dudgeon, 1908, 

 Andrewes and Gordon, 1905-6) that non-pigmented cocci can 



