MICROCOCCUS TETRAGENUS. . 263 



This organism was discovered by Gaffky and was 

 subsequently described by Koch in the account of his 

 experiments upon tuberculosis. It is often present in 

 the saliva of healthy individuals and is commonly 

 present in the sputum of tuberculous patients. Koch 

 found it very frequently in the lung cavity of phthisical 

 patients. It, however, plays no part in the etiology of 

 tuberculosis. 



It is a small round coccus of about 1 // transverse 

 diameter. It is seen as single cells, joined in pairs and 

 in threes, but its most conspicuous grouping is in fours, 

 from which arrangement it takes its name. In prepa- 

 rations made from cultures of this organism it is not 

 rare to find, here and there, single bodies which are 

 much larger than the other individuals in the field. 

 Close inspection reveals them to be cells in the initial 

 stage of division into twos and fours. A peculiarity of 

 this organism is that the cells are seen to be bound to- 

 gether by a transparent gelatinous substance. 



When cultivated artificially it grows very slowly. 



Upon gelatin plates the colonies appear as round, 

 sharply circumscribed, puuctiform masses which are 

 slightly elevated above the surface of the surrounding 

 medium. Under a low magnifying power they are seen 

 to be slightly granular and present a more or less glassy 

 lustre. 



The colonies increase but little in size after the third 

 or fourth day. If cultivated as stab cultures in gelatin 

 there appears upon the surface at the point of inocula- 

 tion a circumscribed white point, slightly elevated above 

 the surface and limited to the immediate neighborhood 

 of the point of inoculation. Down the needle-track 

 the growth is not continuous, but appears in isolated, 



