COMPARATIVE STUDY OF THE COCCI 43 



variety of natural waters public supplies, streams, 

 ponds, pools, shallow wells, driven wells, and the sea. 

 Samples were taken, as far as possible, only from sources 

 considered free from pollution. Under Habitat IV, 

 organisms were isolated from various samples of earth, 

 loam, clay, sand, etc., obtained mainly in different 

 regions of eastern Massachusetts. The cultures grouped 

 under Habitat V were taken from plates exposed to the 

 air of the laboratory or of the city streets; and here are 

 also included certain organisms of unknown origin which 

 appeared as contaminations, or for whose previous history 

 we had no record. 



In each case the sample to be studied was first plated 

 on agar and incubated at 20 degrees. Colonies which 

 looked like cocci (not possessing, for example, the 

 characters of such well-marked forms as B. mesentericus, 

 B. Zopfiij or B. fluorescens), were fished to agar streaks; 

 from each individual source only one culture was taken, 

 unless several distinct types of colonies appeared. The 

 agar streak cultures were examined under the micro- 

 scope and, if apparently cocci, were replated in order to 

 insure their purity, again transferred to agar streaks, and 

 again examined under the microscope. All this pre- 

 liminary work was carried out at 20 degrees, and the 

 stock cultures finally obtained were kept on agar at the 

 same temperature. There can be no doubt that by this 

 method of procedure we failed to obtain many of the more 

 strictly parasitic streptococci which grow only feebly on 



