THE STAPHYLOCOCCUS GROUP 265 



mannite broths. A uniform turbidity is produced in plain and sugar 

 broths; the growth is more luxuriant in the latter. Milk is slightly 

 acidulated, but no coagulation or peptonization takes place. Micro- 

 coccus tetragenus is aerobic, facultatively anaerobic. The optimum 

 temperature of growth is 37 C., the maximum about 44 C., the mini- 

 mum about 12 C. The resistance to physical and chemical agents 

 is undetermined. 



Products of Growth. Unknown: no toxin has been described. 



Pathogenesis. The frequent occurrence of the organism in the 

 sputum of the tuberculous and its occasional isolation from tuber- 

 culous cavities has led to the theory that Micrococcus tetragenus may 

 play a secondary part in the destruction of lung tissue. This is not 

 definitely determined, however. It is also found in the saliva of healthy 

 individuals. Less commonly it has been found in the pus of empyemas 

 which follow pneumonia; but the organism can hardly be regarded 

 as a human pathogen. 



Injected subcutaneously into white mice, Micrococcus tetragenus 

 usually causes a fatal septicemia; the organism may be recovered 

 from the heart blood, spleen and liver. House and field mice appear 

 to be relatively immune. Intraperitoneal injection into guinea-pigs 

 may cause a fatal peritonitis with much pus in which typical tetrads 

 are found. Rabbits and dogs are not .susceptible. Infections with 

 the organism in man are so uncommon that nothing is definitely known 

 of human susceptibility and immunity. Vaccines have been tried 

 in a very few cases with somewhat promising results. 



Bacteriological Diagnosis. The finding of Gram-positive cocci about 

 1 micron in diameter in pus, which occur habitually in tetrads, usually 

 suffices to establish a satisfactory bacteriological diagnosis. The 

 saliva occasionally contains tetracocci which resemble Micrococcus 

 tetragenus very closely, but it is claimed by many that these organisms 

 are not necessarily Micrococcus tetragenus, Isolation and identifica- 

 tion by cultural methods must be resorted to in suspected cases. 



Micrococcus Ovalis. Synonym. Enterococcus. 1 



Historical. Micrococcus ovalis was described by Escherich, 2 who 

 found it very commonly in the intestinal tracts of nurslings and bottle- 

 fed infants. 



Morphology. The organism is oval in outline, measuring 0.6 to 

 0.9 microns in the lesser diameter, and it occurs habitually in pairs, 



1 Thiercelin, Th&se de Paris, 1894. 



2 Darmbakterien des Sauglings, Stuttgart, 1886, p. 89. 



