BACTERIOLOGICAL INTRODUCTION 15 



generally greatly dependent on the conditions under 

 which the organism is living. It generally dis- 

 appears in artificial cultures, and is best seen in the 

 secretions or tissues of the infected animal. These 

 remarks apply to most capsulated organisms. 



It will be noticed that the capsule surrounds the 

 group. Cocci collected into irregular groups sur- 

 rounded by capsules are sometimes called asco-cocd. 

 Beside the tetrad groups there appear in the pre- 

 paration groups of two organisms. These probably 

 represent the tetrad viewed from the side, or, in 

 some cases possibly a group in which the division in 

 the two axes has not been synchronous. 



(e) Sarcina. — To this group belong those organisms 

 which form groups of eight cells by a triaxial division 

 of the original cell by planes at right angles to one 

 another. The unit of division in this sub-group is a 

 packet of eight. Such an organism is shown in 

 Fig. 6. At first sight this would appear to belong 

 to the preceding group, but this appearance is due to 

 the impossibility of photographing organisms on two 

 planes, and the consequent necessity for choosing a 

 place in the specimen where the groups have been 

 dissociated. The thickly-stained group on the left, 

 and still better, the group on the extreme right of 

 the specimen indicates the true character of the 



