INFECTIOUS DISEASES AND MICROBES, ETC. 237 



Bacillus diphtherias (No. 2) gives rise to greyish 

 dots after 36-48 hours' incubation at 20 C. After 

 three or four days, these appear as white round 

 convex droplets, which ultimately aggregate together 

 forming yellowish -brown colonies. Colonies are 

 also formed when the microbe is grown as a plate- 

 cultivation (Fig. 46 C). In alkaline bouillon, B. 

 diphtherice gives rise to a turbidity in twenty-four 

 hours after inoculation; and afterwards a greyish- 

 white precipitate is produced at the bottom of the 

 tube. 



In milk kept at 18-20 C., this microbe grows 

 very rapidly. The milk always remains fluid ; but 

 in two or three days after inoculation, flakes of 

 casein separate. 



B. diphtherice (from 3 to 6 /z, long) does not pro- 

 duce spores ; but it gives rise to a soluble enzyme 

 and one or more ptomaines. Drs. Eoux and Yersin l 

 isolated an enzyme, from a pure cultivation of the 

 microbe in question, which produces all the symp- 

 toms of diphtheria. This is a true enzyme, for 

 boiling water destroys its action. 



The author 2 extracted a ptomaine (C 14 H 17 N 2 6 ) 

 from urine in cases of diphtheria; and the same 

 ptomaine was also obtained from pure cultures of 

 B. diphtherice on peptonised gelatine. This ptomaine 

 is not present in normal urine. Brieger and 

 Fraenkel 3 have also isolated a toxalbumin from 



1 Annales de VInstitut Pasteur, 1888. 



2 Griffiths in Comptes Rendus, vol. cxiii. p. 656 ; Nature, 

 vol. xlv. p. 72. 



3 Berlin Klin. Woch., Bd. xxvii. pp. 241 and 1133. 



