170 BACTERIOLOGY 



ward, corresponding to the track of the needle; at times a 

 stocking- or sac-like liquefaction may be noticed. (See 

 Fig. 32.) 



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, actively 

 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 containing each about 10 c.c. of: 



Gelatin 7 . 00 grams 



Phenol . 25 gram 



Water 100. 00 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 

 the solid gelatin. To the tube of liquefied gelatin add like- 

 wise 0.5 c.c. of the heated culture, mix it thoroughly with 

 the gelatin, and place the tube containing the mixture 

 in cold water until the mass becomes solid. Set both tubes 

 aside at a temperature not above 20 C. Note what occurs 

 at the end of an hour, by next day, and after three days. 

 Alter the experiment by filtering the three-day-old bouillon 

 culture through a porcelain- or a Berkefeld filter, instead of 

 heating it as directed above. Are the results modified? 

 How do you interpret these results? 



