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A MANUAL OF BACTERIOLOGY 



II. The membrane is frequently so crowded with different 

 forms of organisms that it is extremely difficult to recognise the 

 diphtheria bacilli with any degree of certainty. Kecourse must 

 then be had to cultivation. 



For this purpose sloping blood-serum tubes (best), tubes of 



C = coagulation ; = no coagulation ; A = acid ; no reaction. 

 Slight variations were occasionally noted ; for example, four out of twenty 

 diphtheria bacilli gave no acid with lactose, and the amount of acid produc- 

 tion and of coagulation was somewhat variable. 



serum -agar, or agar smeared with blood must be employed ; 

 simple agar is unsuitable. 1 



1 Various selective media have been devised, e.g. potassium sulpho- 

 cyanide neutral-red glucose blood-serum (Rankin, Journ. of Hyg., xij, 

 1912, p. 60), 



