1 6 LABORATORY BACTERIOLOGV 



21. Inoculating Tubes of Gelatin. — Tube cultures in gela- 

 tin are usually made without inclining the gelatin, i.e. stick 

 cultures. The tube of gelatin is inoculated in the same man- 

 ner as the stick culture in agar. This tube is to be placed in 

 the locker, as the gelatin will melt at the incubator temperature. 

 The growth will appear in about two days along the needle 

 track. This is a gelatin culture of B. colt communis. 



22. Sealing Culture Tubes. — It is often desirable to seal 

 cultures to prevent their drying out quickly. A convenient 

 method, and one which has long been in use in some laborato- 

 ries, is to boil a small quantity of paraffin in a small agate iron 

 dish, and while it is still hot carefully dip the tube end of the 

 plug into it and quickly replace it in the tube. The paraffin 

 on cooling adheres to the sides of the tube, forming a tight 

 plug. When the tube is to be opened, the end must be warmed 

 slightly before the plug can be withdrawn. The plugs should 

 be paraffined and the sterility of the tubes determined before 

 they are used for cultures. 



