COMPARATIVE STUDY OF THE COCCI 49 



recorded on the tenth day, after which time each was 

 transferred to gelatin and examined after one day. The 

 results showed no significant differences. 



In a comparison of size, as determined by examina- 

 tion of living organisms and of stained preparations, the 

 cells appeared generally somewhat smaller after stain- 

 ing. This is no doubt partly due to shrinkage in 

 drying and partly to the imperfect definition which 

 makes the unstained specimens appear larger than they 

 really are. Occasionally, when the staining was too 

 heavy, the stained cells appeared larger. In any case 

 the differences are unimportant; and we have used the 

 size of the methylene-blue stained preparation through- 

 out our work. 



Staining reactions. Since the cocci, as far as we have 

 examined them, all stain easily with methylene-blue, we 

 made no special tests with anilin-gentian-violet. The 

 Gram stain was, however, used on all our cultures, 

 since in the genus Diplococcus and in many other groups 

 it has special importance. 



The value of this staining method was studied with 

 considerable care by Mr. A. T. Brant, working in the 

 laboratories of the Institute. Mr. Brant found, as other 

 observers have done, that while certain bacteria are con- 

 stantly Gram-negative, or Gram-positive, others exhibit 

 an intermediate condition, retaining the stain under some 

 circumstances and giving it up under others. He noted, 

 for example, that all cultures of B. coli are decolorized 



