36 RELATIONSHIPS OF THE COCCACE^ 



and their pigment production and general vigor of growth. 

 By using these characters, with one or two others which 

 were of importance in special cases, we made a tenta- 

 tive grouping of the 445 described forms under 3 1 types 

 (Winslow and Rogers, 1905). 



Some of the 31 types, recognized from the literature, 

 in this preliminary communication, have since proved to 

 be artificial in view of a comparative study of the cocci 

 themselves. The main points brought out at the early 

 stages of the investigation still, however, seem to us well 

 founded. Among these, was the conclusion that the 

 family as a whole may be divided into two main groups, 

 one of parasitic, the other of saprophytic habit. Patho- 

 genic power is one of the properties which vary most 

 easily among the bacteria; and from the systematic 

 standpoint it has appeared to Migula (1897) and others 

 to be of slight importance. Nevertheless, it is quite 

 clear that certain well-defined natural groups of bacteria 

 are generally associated with the peculiar environment 

 offered by the epithelial surfaces of the animal body. 

 It is necessary to make a distinction between parasitism 

 and pathogenicity. The parasitic habit, the adaptation 

 to life on the body surfaces of the higher animals, marks 

 off certain important groups of the bacteria. Within 

 these groups the actively pathogenic forms and those 

 which live harmlessly on the epithelia are closely related. 

 Among the Coccaceae particularly, the pathogenic pow- 

 ers appear to come and go with special ease; but the para- 



