32 BACTERIOLOGY. 



atmospheric germs on removal from the ordinary 

 test-tube of the cotton wool plug. Each test-tube 

 is provided with a lateral arm tapering to a fine 

 point, which is hermetically sealed. 



Drop-culture Slides. About a dozen or more 

 thick glass slides with a circular excavation in the 

 centre are required for drop-cultures. 



Vaseline. A small pot of vaseline with a 

 camel's hair brush should be reserved especially for 

 use in the preparation of drop-cultures. 



Bulbed Tubes. Glass vessels such as test- 

 tubes, flasks, and pipettes, which are used in 

 dealing witlr liquid media, have already been 

 mentioned under other headings, but bulbed tubes, 

 Pasteur's bulbs, and various other forms are also 

 required for special experiments. 



(L) APPARATUS FOR INCUBATION. 



There are several forms of incubator, each of 

 which has its advocates. They are mostly rec- 

 tangular chests, with glass walls, front and back, 

 or in front only. A cylindrical model is preferred by 

 some. Two only will be described here, D'Arsonval's 

 and Babes'. The former admits of very exact 

 regulation of temperature, and the latter is a very 

 practical form for general use. 



D'Arsonval's Incubator. The " tuve HAr- 

 sonval" (Fig. 16) is a very efficient apparatus, 

 and is provided with a heat regulator, which 



