13 



the dextrose, acid was formed and this acid inhibited the proteolytic 

 action. Whether or not the presence of dextrose or the acid produced 

 from dextrose prevents the formation of the proteolytic enzyme is not 

 evident from these experiments, though it seems probable that dextrose 

 alone would not be capable of exerting such an influence. 



B. cloacae, unlike P. vulgar is, is able to liquefy gelatin in the 

 presence of all the sugars tried. It was noted, however, that the lique- 

 faction in the case of B. cloacae did not begin as quickly in the 

 sugar gelatin tubes as in the nutrient gelatin tubes, though when it did 

 begin it proceeded further in some cases. An initial acid production 

 takes place in sugar gelatin tubes inoculated with B. cloacae since 

 litmus added to these tubes turned red after 48 hours incubation at 

 22 C. Evidently, a small amount of acid does not interfere with the 

 proteolytic action of B. cloacae to any great extent. Since it was 

 shown in a previous paper (33) that the initial acidity produced by 

 B. cloacae in a sugar protein medium may be followed by alkalinity, 

 it is possible that the amido compounds produced by the proteolytic 

 action of this organism tend to neutralize the acid produced, and thus 

 keep the percentage of acid low enough to enable the proteolytic ferment 

 to work, or the proteolytic ferment of B. cloacae may be more resistant 

 to acid than is the ferment of P. vulgar is. This is suggestive that 

 the proteolytic ferment of B. cloacae is more peptic than tryptic. 



An attempt was made to cause the non-gelatin liquefiers to liquefy 

 gelatin by growing them in nutrient gelatin for varying lengths of time 

 under different degrees of temperature. Some gelatin cultures were 

 placed in the 37 incubator and allowed to remain there for six days. 

 The gelatin was then placed in the ice box to see if it would solidify 

 again. The tubes on solidifying, were plated out in gelatin and ten 

 characteristic colonies were selected and inoculated into gelatin tubes. 

 These were allowed to stand for six days and again plated out and 

 selections made from the colonies on the plate. Although this process 

 was carried on through several transfers, not a single culture was 

 obtained which would liquefy nutrient gelatin when allowed to stand 

 at 22 for 30 days. All the gelatin tubes inoculated with the non- 

 liquefiers and kept in the 37 incubator solidified again when placed in 

 the ice box for a short time. The colonies on the gelatin plates were 

 characteristic only when the gelatin was moist. If the percentage of 

 gelatin in the medium was high, the characteristic Proteus colonies 

 did not always develop. 



The fact that Proteus Zenkeri and Proteus mirabilis do 

 not liquefy gelatin readily or at all is hardly sufficient reason to classify 

 these organisms as species distinct from Proteus vulgaris. Some 

 authors have made the observation that a species of P. Zenkeri which 

 had repeatedly failed to liquefy gelatin suddenly developed this power, 

 while Smith (5) was able to obtain a non-gelatin liquefier from P. 

 vulgaris. These facts would indicate that P. Zenkeri and P. mira- 

 bilis and Zopfii are varieties of P. vulgaris which have lost many 

 of their enzymotic powers but have developed no new characteristics 

 which would be sufficient to call them distinct species. P. Zopfii and 

 P. Zenkeri, together with the strains of P. mirabilis which do not 

 liquefy gelatin, all belong undoubtedly to the same variety, P. Zenkeri, 

 and the names Zopfii and mirabilis could very well be- done away 

 with. The strains of P. mirabilis are at best intermediate forms 



