EXAMINATION OF LIVING BACTERIA. 25 



ing drop, it is possible that roundish cells may again 

 be found, which even with the microscope can hardly 

 be distinguished from the first ones. But the naked- 

 eye appearance of the colonies was quite different, the 

 first being perhaps white, and the second yellow. We 

 observe, therefore, that these characteristics of form 

 are not sufficient in themselves to distinguish the 

 different species from one another, and that, in addi- 

 tion to the morphological characteristics, we must 

 take the culture characteristics into account. A third 

 colony may have the same yellow colour as the second, 

 whilst appearing somewhat drier. If we spread out a 

 small portion of it in the hanging drop, we find with 

 the microscope quite another effect. The single cells 

 may be roundish again, but they cling together in 

 eights, or in multiples of eight, forming compact ball- 

 like little bundles. We should then have a specimen of 

 the species Sarcina (wool-pack fungus) , which belongs 

 to the group Cocci, or ball-bacteria, but which forms 

 a genus by itself. We are not likely to come across 

 a third genus, Merismopedia, as it is comparatively 

 rarely met with. In this genus the cells join together 

 in packets of four, or of a multiple of four ; but the 

 packets are not, as in Sarcina, several layers thick, 

 but only one layer thick. This genus is also called 

 Merista. 



On the other hand, we are very likely to find several 

 different varieties of the genus Micrococcus. If the 



