14 



between vulgaris and Zenkeri, which need but cultivation to turn 

 them into P. vulgaris on the one hand or P. Zenkeri on the other. 

 The morphological characteristics are of little use in the differentiation 

 of these organisms since under artificial conditions either may produce 

 short rods or longs filaments, according to the kind of media used and 

 the condition under which they are grown. P. vulgaris in all strains 

 was negative to Gram, while P. Zenkeri was usually positive, but 

 even this characteristic is so variable that it has no characteristic value. 

 None of the species of Proteus examined produced any pigment. 

 This test was made on potato, Heinemanns synthetic medium, and 

 on agar, to which 1 % of tyrosin had been added. In the latter medium, 

 P. vulgaris produced a dark coloration in the medium in about 24 hours, 

 but no pigment was developed. 



Conclusions. 



1. Selection of slight variations in acid production in sugar broth 

 by P. vulgaris tailed to produce any variation in the acid producing 

 properties of this organism. 



2. P. vulgaris, though not able to ferment lactose under aerobic 

 conditions, does so when cultivated under anaerobic conditions. 



3. Carbohydrates, when fermented by P. vulgaris or B. coli, 

 inhibit the production of indol, by these organisms. The inhibition is, 

 however, due to the acid formed and not to the carbohydrate itself. 



4. The addition of more than 0,5 % f lactic acid to the culture medium 

 inhibits the production of indol. 



5. The acid formed by the fermentation of carbohydrates inhibits to 

 a certain degree the liquefaction of gelatin by members of the Proteus 

 group. 



6. The ferment formed by P. vulgaris seems to be a tryptic 

 ferment, while that of B. cloacae is suggestive of a peptic ferment. 



7. P. Zopfii and Zenkeri are probably one and the same variety, 

 and P. mirabilis seems to be an intermediate form between Zenkeri 

 and vulgaris which differs in the intensity of its biochemical reactions, 

 but not in the quality. Some strains of mirabilis examined gave similar 

 biochemical reactions to those of P. Zenkeri, while others resembled 

 P. vulgaris very closely. 



The writer takes great pleasure in thanking Professors E. 0. Jordan 

 and Norman MacL. Harris for their suggestions and encouragement 

 in this work. 



References. 



1) Ann. d. Tlnst. Pasteur. Vol. 6. 1892. p. 512. 



2) Zeitschr. f. Hyg. Bd. 17. 1894. p. 1. 



3) Lancet. Vol. 11. 1906. p. 708. 



4) Journ. Boston Soc. Med. Sc. Vol. 4. 1900. p. 170. 



5) Journ. Exper. Med. Vol. 2. 1897. p. 543. 



6) Journ. Exper. Med. Vol. 2. 1897. p. 549. 



7) Proc. Eoy. Soc. Vol. 79. 1897. p. 320. 



