166 BACTERIOLOGY. 



the solid gelatin. To the tube of liquefied gelatin add 

 likewise 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 inter- 

 pret these results ? 



