GELATINE TUBES 87 



carefully, and heat for another half -hour, stirring it from 

 time to time. 



(5) Then add the white of an egg, and continue heating 

 till all the albumen is precipitated. 



(6) Filter through a hot- water funnel with two layers of 

 moistened filter-paper into sterilised flasks, and sterilise in 

 the steamer on two successive days for twenty minutes. 1 



To fill tubes with gelatine : 



Melt the gelatine and pour it into a sterile separating 

 funnel, and proceed as described for broth-tubes (vide p. 84). 



The gelatine tubes must be sterilised in the steamer on 

 two successive days. 



After the last sterilisation, place some of the tubes, 

 while still liquid, on a sloped tray and allow the gelatine 

 to set in this manner (for streak cultures). Allow the others 

 to set in an upright position (for stab cultures and plates). 



V. GRAPE-SUGAR GELATINE. 



(1) In every 100 cc. of liquid gelatine dissolve 2 grammes 

 of grape-sugar. 



(2) Fill test-tubes, and sterilise on two successive days 

 in the usual manner. 



VI. 25 PER CENT GELATINE. 



(1) To every 100 cc. of liquid 10 per cent gelatine add 



1 Gelatine must not be heated too much nor too long, since by so 

 doing it may lose its property of setting when cold. The gelatine 

 should be quite clear. If it be turbid after sterilisation, this is often 

 due to the fact that it is too alkaline. In such a case add lactate of 

 ammonium, not hydrochloric or nitric acid. 



