170 BIOLOGY AND TECHNIQUE 



kept in stoppered sterile bottles and added to agar as desired. This 

 is particularly useful in preserving blood for routine work on menin- 

 gococcus carriers. 



Methods of bleeding animals are briefly described above. 



SELECTIVE ACTION OF DYE STUFFS 



In describing the selective media for typhoid bacilli we have 

 seen that malachite green and crystal violet have been found to 

 exert a certain amount of selective action upon the typhoid and 

 colon groups. The selective influence of various dyes has been 

 recently again studied by Churchman. Churchman 46 found that the 

 addition of gentian violet in dilutions of 1 :100,000, to media, in- 

 hibited some bacteria, while others grew luxuriantly in its presence. 

 Extremely interesting, both practically and theoretically, is his ob- 

 servation that upon such gentian violet media bacteria fall into two 

 groups. Those which grow on gentian violet correspond in a general 

 way to the Gram-negative bacteria; those which fail to develop on 

 these media correspond roughly with the Gram-positive species. 

 One strain of the enteritidis group could not be cultivated on gen- 

 tian violet, and this was found to differ from the others also in its 

 agglutination tests. 



Signorelli 47 claims that dahlia is useful in differentiating true 

 cholera strains from similar spirilla. The true cholera strains grew 

 with colored colonies, while others remain colorless, in his experi- 

 ments. 



Krumwiede and Pratt 48 were unable recently to confirm the 

 claims of Signorelli. However they fully confirm the findings of 

 Churchman both as to the selective action of gentian violet and in 

 regard to the classification of bacteria into two groups corresponding 

 to their reaction to the Gram stain. They state that among Gram- 

 negative bacteria a strain is occasionally found which will not grow 

 on the gentian violet media, differing in this respect from other 

 members of the same species. They find also that the reaction is 

 quantitative. 



The streptococcus-pneumococcus group, according to their in- 



* Churchman, Jour. Exp. Med., 16, 1912 ; also Churchman and Michael, ibid. 

 "Signorelli, Centralbl. f. Bakt., Orig. 56, 1912. 



"Krumwiede and Pratt, Centralbl. f. Bakt., Orig. 68, 1913; and Proc. N. Y. 

 Path. Soc., xiii, 1913. 





