58 RELATIONSHIPS OF THE COCCACEyE 



determination. We should, of course, deprecate any 

 extension of this conclusion to other groups where the 

 gelatin stab or the plate culture may yield information 

 of definite value. In the absence of evidence as to the 

 significance of agar and gelatin plates, potato cultures, 

 etc., it seems unwise to repeat tests mechanically and 

 without any definite purpose, merely because they have 

 had an important place in the historical development 

 of the science. 



Therefore, in our work, all cultural characteristics 

 were observed in the agar tube. A combined streak 

 and stab was made on a slant surface, and the cultures 

 were uniformly studied after incubation for two weeks 

 at 20 degrees centigrade. Cultures of different age exhibit 

 marked differences, but the characters of the old culture 

 are the outcome of those of the new. Comparative studies 

 with lactose agar and glycerin agar showed neither to 

 be as favorable a medium as ordinary nutrient agar. 



In order to obtain a comparative idea of cultural 

 characters, we examined agar streak cultures, two weeks 

 old, made from the whole 500 strains at the same time. 

 The visible differences between the cultures were due 

 almost wholly to two properties, — chromogenesis and 

 general vigor of surface growth. There was a dis- 

 tinction in luster between a large majority of the cul- 

 tures which had smooth and shining surfaces and a few 

 which were dull and rough. This difference appears, 

 however, to be due mainly to the relative amount of growth 



