MICROCOCCI 221 



plate, (4) gelatin stab plate and slope, (5) milk, (6) potato, 

 (?) peptone water, (8) nitrate, and (9) sugar media. 



In broth, uniform turbidity with thin surface, pellicle 

 ultimately settling as a heavy mucoid deposit, with a sour 

 odour like weak butyric acid. 



On agar slope, abundant growth in 24 hours at 37 C. ; 

 with smooth shining surface and resembling a streak of 

 oil paint. Single colonies are circular. 



On agar plate, numerous small, shining, pin-head shaped 

 colonies; round, finely granular, with smooth edges, 

 remaining discrete, and varying greatly in size. 



On gelatin plate, growth occurs readily at 20 C., and 

 shows much the same as in agar. The colonies are not 

 flat, but rise from the surface as the segment of a sphere. 

 Liquefaction of the gelatin ; and gradually (after 48 hours 

 or more), shallow saucer-shaped depressions are formed, 

 which grow larger and finally become confluent. Lique- 

 faction of gelatin by staphylococci is due to a ferment-like 

 body elaborated by them and spoken of as " gelatinase " 

 and which can be obtained apart from the cocci by 

 filtration of cultures. It is an extremely thermolabile 

 substance. 



In gelatin stab, a streak of growth is visible in 24 hours, 

 and liquefaction begins at the top in 2 to 3 days, forming 

 a funnel with flocculent deposit of the bacteria. Ultimately 

 fluidification extends to the wall of the tube. 



In milk, coagulation takes place in 3 to 4 days with 

 formation of lactic and butyric acids. 



On potato, growth is abundant, rather dry, and 

 usually deeply pigmented. 



In peptone water, indol is formed. 



Pigment formation is best seen in serum or starchy 

 media and aerobically only. It is insoluble in water but 

 soluble in alcohol, chloroform, ether, and benzol. It is 

 a C, H, and O compound, a " lipochrome ", or fatty pig- 

 ment. Strong H 2 SO 4 changes it to green or green-blue. 



Toxic Products. Endotoxins, haemolysins, leucocidins. 



Pathogenicity. For man : abscesses, boils, carbuncles, 

 endocarditis, osteomyelitis ; for animals : rabbits most, 

 mice medium, guinea-pigs least. 



Immunization. Take three-weeks-old culture, heat at 



