SYSTEMATIC AND DESCRIPTIVE. 121 



tetrads, and in packets. A single individual in a 

 tetrad may be divided into two, or into four, so 

 that a tetrad within a tetrad results. Cultivated 

 in nutrient agar-agar in a test-tube, they form a 

 colourless growth along the track of the needle, 

 and a bright, canary-yellow layer upon the surface, 

 where they have access to the air (Plate XIII., 

 Fig. i, Plate VIII., Fig. i). In plate-cultivations the 

 colonies are round, slightly granular in appearance, 

 and yellow. Cultivated in a test-tube containing 

 nutrient gelatine, they grow rapidly, the gelatine 

 becoming liquid, the yellow growth forms a wad 

 about the middle of the tube (Plate V., Fig. 2), or, 

 liquefying the whole of the gelatine, subsides to 

 the bottom of the test-tube. Cultivated on sterilised 

 potatoes they form a yellow layer (Plate X., Fig. i). 

 In drop-cultures in bouillon the subdivision into 

 tetrads within tetrads and formation of groups of 

 8, 1 6, and 24 can be studied (Plate I., Fig. 7). In- 

 oculation of mice produces negative results. The 

 cocci are occasionally present in the air. 



Sarcina urinae, Welcker. Very small cocci, 

 1*2 p. in diam., united in families of 8 to 64. 

 Observed in the bladder. 



Sarcina litoralis, Oersted. Cocci 1-2 2 /x, in 

 diam., bound together in 4 to 8 families, which, in 

 their turn, may unite and include as many as 64 

 tetrads. Plasma colourless ; in each cell i 4 

 sulphur granules. Discovered in sea-water con- 

 taining putrefying matter. 



