TEST-TUBE, STAB- AND SMEAR-CULTURES. 165 



been introduced into it possesses the power of bringing 

 about liquefaction i. e., of digesting it it will soon be 

 discovered that the mode of liquefaction differs with 

 different organisms and is practically constant for the 

 same organism. Some bacteria cause a liquefaction 

 which spreads across the whole upper surface of the 

 gelatin and continues gradually downward ; with others 

 it occurs in a funnel-shape, the broad end of the funnel 

 being uppermost and the point downward, correspond- 

 ing to the track of the needle ; at times a stocking- or 

 sac-like liquefaction may be noticed. (See Fig. 33.) 



NOTE. Obtain a number of organisms from different 

 sources in pure cultures by the method given. Plant 

 them as pure cultures, all at the same time, in gelatin 

 preferably gelatin of the same making retain them 

 under the same conditions of temperature, and sketch 

 the finer differences in the way in which liquefaction 

 occurs. 



Select from your collection a non-spore-bearing, ac- 

 tively liquefying species. Cultivate it as a pure culture 

 in nutrient bouillon for three days. Then heat this 

 bouillon culture to 68 C. on a water-bath for ten 

 minutes. In the meantime prepare several tubes con- 

 taining each about 10 c.c. of: 



Gelatin 7 grammes. 



Phenol 0.25 gramme. 



Water 100 c.c. 



Let the carbolized gelatin in one tube remain solid, and 

 bring that in another to a liquid state by gentle heat. On 

 the surface of the gelatin in the first tube place 0.5 c.c. of 

 the heated (and cooled) culture, and mark on the side of 

 the tube the point of contact between the fluid culture and 



