i62 C.-E. A. WiNSLow AND Anne F. Rogers 



Among the liquefying forms we have not found the shape of the 

 liquefaction of sufficient constancy to be recorded. Whipple (1902) 

 has strikingly shown the uncertainty of this character — almost every 

 possible type appearing in media made with slightly different com- 

 mercial gelatins. The Committee on Standard Methods (1905) has 

 also omitted this property. 



The amount of liquefaction of gelatin was therefore the only 

 character recorded on the gelatin stab. The method by which this 

 was measured will be described under "Biochemical Reactions." 



Agar plates. — The same reasons which led us to omit the gelatin 

 plate militate against the use of the agar plate as a diagnostic test. 

 Constant differences which exist between colonies are slight and 

 depend on a few fundamental properties which may be more easily 

 observed on other media, notably on the agar streak. 



Agar tubes. — The general conclusion from what has been said 

 in this discussion of cultural characteristics is that in the cocci a 

 single medium is sufficient for their determination. We should, 

 however, deprecate any extension of thiS" conclusion to other groups 

 where the gelatin stab or the plate culture may yield information of 

 definite value. Even among the cocci further study may show con- 

 stant and characteristic differences in gelatin colonies, and if this 

 should be the case, no one could fail to welcome an addition to the 

 meager list of diagnostic characters at our disposal. In the absence 

 of evidence as to the value of these media, we feel it 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. 



All cultural characteristics have therefore been observed in the 

 agar tube. A combined streak and stab was made on a slant sur- 

 face, and the cultures were uniformly studied after incubation for 

 two weeks at 20° C. Cultures of different age exhibit marked differ- 

 ences, but the characters of the old cultures 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 two weeks' agar streaks of the whole 500 cultures 



