136 



Edwin O. Jordan 



bacterial gelatinase must exercise its effect almost exclusively in an 

 acid medium. 



The change in the reaction of the medium, as might be expected, 

 is not confined to the hquefied gelatin, but is communicated by diffu- 

 sion to the yet unliquefied portions. 



EXPERIMENT. 



Two hundred c.c. of 10 per cent nutrient gelatin (neutral) were placed in 600 c.c" 



flasks. These were inoculated on one side and the flasks tipped so that liquefaction 



took place in only one-half. After incubation at 20° C. for four days the liquefied 



gelatin was drawn off and the reaction of this and of the unliquefied portion determined. 



B. amyloruher. 



Liquefied gelatin i . 8% acid 



Solid gelatin 0.7 " 



B. suUilis. 



Liquefied gelatin 2 . 9% acid 



Gelatin removed from directly under liquefied area . . .0.9 " 



Gelatin taken 3 cm. from liquefied region 0.6 " 



Gelatin from opposite side of flask 0.4 " 



Perhaps one reason why the standardization of nutrient gelatin for 

 plate cultures has not been so successful as could be desired is because 

 after growth begins alterations in reaction occur in varying degrees 

 according to the relative abundance or scarcity of hquefying species. 



It follows, too, that the reactions produced by bacteria in ordinary 

 broth are dependent, not only upon the presence of sugar, but to a 

 degree upon the amount of gelatin and similar substances in the 

 medium. 



EXPERIMENT. 

 Neutral gelatin was inoculated with B. pyocyaveus and the filtrate was found 

 after four days at 37° C. to be i .8 per cent acid. The action of the filtrate (18 hrs.) 

 upon carbol gelatin of different degrees of alkalinity was as follows: 



Amount of Filtrate 



1.8% Acid- 

 0.5 c.c. 

 o 

 o 

 o 

 o 

 o 



2% 



o 

 o 

 o 

 o 

 o 

 o 



3 



I 



05 



03 



Alk. witii N/V NaOH— ' 

 5 c.c 



3 



I 



05 



03 



01 



Carbol Gelatin 



0.7% Acid 



+ 

 + 

 + 

 + 

 ± 

 o 



Neutral 



+ 

 ± 



± 

 ± 

 ± 



o 

 o 



0.7% Alk. 



+ 



o 

 o 



± 

 ± 



o 

 o 

 o 



o 



