CHAPTER III. 



METHODS ADOPTED IN. THE COMPARATIVE STUDY 

 OF THE COCCI. 



The general relationships, discussed in the last chap- 

 ter, were suggested by the descriptions of Coccaceae 

 available in the literature. In order to establish our 

 conclusions, and to extend the analysis to smaller 

 groups, it was necessary to carry out a comparative 

 study of a considerable series of cultures of cocci 

 from various sources. Such a study, covering 500 dif- 

 ferent strains of cocci, was made in 1905-06. Our aim 

 was to observe as many definitely measurable characters 

 as possible; to find the centers of variation marked by 

 the modes of the frequency curves obtained; and to 

 discover the correlations existing between the various 

 characters. According to the views set forth in Chapter I, 

 we believed that each distinct center of variation could 

 be considered as marking a specific type, while the 

 species which were identical in several correlated char- 

 acters could be considered as forming a single genus. 

 The general results of this investigation have been 

 already published (Winslow and Rogers, 1906), in brief 

 form. 



We included in our study representatives of only three 



