BY R. GREIG SMITH. 341 



the gelatin. In the presence of dextrose or galactose the latter 

 is almost overcome by the former, but with other sugars the 

 hardening and darkening substance is not produced. When the 

 gelatin is hardened, the growth is always scanty, as if the active 

 substance were an antiseptic like formaldehyde. 



The hardening substance does not appear to be formed in fluid 

 cultures, for when various cultures of the bacterium, such as 

 Hansen's fluid, meat-extract bouillon, saccharose-peptone fluid, 

 dextrose-asparagin fluid, were added to a solution of gelatin no 

 hardening was obtained; the test in every case melted at the 

 same temperature as the control. 



The liquefaction appears to proceed slower than the hardening, 

 as the liquefied gelatin can be removed from above the dark 

 medium by carefully washing it with water and the unhardened 

 gelatin by slowly raising the temperature and removing the 

 medium as it liquefies. The portions at the bottom of the 

 tube as well as the top parts of the slope as a rule remain in 

 those cases in which the liquefaction has made a slight headway. 

 It is only when the medium is very dark that the hardening 

 effect can be clearly demonstrated. When the tube is placed in 

 boiling water, the upper portion of the gelatin slope in some 

 cases separates from the glass and appears to be of a horny 

 nature, while the medium at the lower part of the slope seems to 

 be somewhat flabby. 



The effect was obtained readily when the microbe had been 

 recently isolated, but after the lapse of nearly a year the bacterium 

 had so far increased the relative production of the liquefying 

 enzyme that one had to adopt means for circumventing the lique- 

 faction. These consisted in growing the bacterium upon glucose- 

 gelatin in the air for a day or two until the darkening had made 

 a slight headway and then putting the culture tube into a 

 Buchner tube. In about three weeks the medium had become 

 uniformly dark and almost black-brown. In some cases the 

 medium at the lower part of the stroke, although apparently soft, 

 had not liquefied, and in placing the culture tube in water at 40° 

 about 5 CO. of the soft medium liquefied ; upon this being 



