16 LABORATORY BACTERIOLOGY 
V 22. Inoculating tubes of gelatin. Tube cultures in gela- 
tin are usually made without inclining the gelatin, i.e. stab 
cultures. The tube of gelatin is inoculated in the same man- 
ner as the stab culture in agar. This tube is to be placed in 
the locker, as the gelatin will melt at the incubator tempera- 
ture. The growth will appear along the needle track in about 
2 days. This is a gelatin culture of 2. col. 
23. 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 labora- 
tories, is to melt 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 fills the spaces between the fibers of cotton 
and also 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slightly before the plug can be withdrawn.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. 
