170 C.-E, A. WiNSLow AND Anne F. Rogers 



white — are pretty certain to occur. We have therefore included 

 chromogenesis as one of our routine tests. The variations due 

 to past and present environment are, of course, easily excluded by 

 the maintenance of constant conditions. Our stock cultures were 

 in all cases kept on agar at 20°, and cultures for chromogenesis 

 were grown on that medium, and at that temperature, for two weeks. 

 In order to avoid the apparent differences due to the vigor of growth 

 or to evaporation, a portion of the growth was removed on a loop 

 needle and spread out on white drawing-paper with a rough surface. 

 After drying at the room temperature, the color was compared with 

 an arbitrary standard scheme. 



The color chart used for matching these colors was devised after 

 a very careful study of the colors actually found among the Cocca- 

 ceae, and includes nine hues ranging from white through lemon-yel- 

 low, light cadmium, medium cadmium, lemon-yellow and cadmium 

 orange, red and cadmium orange, to two different combinations 

 of red with lemon-yellow. We have used under each hue, nine differ- 

 ent chromas, obtained by successively increasing washes of the hues 

 on white paper. The hue in each case is recorded by a Roman 

 numeral; the chroma, or number of wash, by an Arabic subscript. 



Liquefaction 0} gelatin. — The liquefaction of gelatin, like the prop- 

 erty of pigment production, has been shown to be subject to fluctu- 

 ating variations. Conn (1900) was able by selection to obtain from 

 a single culture of a milk coccus a rapidly liquefying form, and 

 one with almost no peptonizing power. Smith (1900) records 

 similar experiences with colon bacilli and forms of B. proteus. There 

 appears to be little correlation between hquefaction and any other 

 power, since it is so common in widely separated groups of bac- 

 teria to find organisms differing in this respect, while identical in 

 all other properties. 



In studying liquefaction we have determined only the amount 

 of the action exerted by each organism. The shape of the liquefac- 

 tion in the stab culture has been shown by Whipple (1902) to vary 

 within the widest limits, with slight differences in the character 

 of the medium, and the Committee on Standard Methods (1905) 

 has omitted this character from its list. 



For determining the amount of liquefaction we have used the 



