624 



APPENDICES. 



(G) Apparatus and Material for Preparing and Storing 

 Nutrient Gelatine and Nutrient Agar-agar. 



Water-bath. — A water-bath on tripod stand is required for 



boiling the ingredients of nutrient jellies and for general purposes. 



The lid may be conveniently composed of a series of concentric 



rings, so that the mouth of the vessel may be graduated to any 



size required. 



Test-tube Water-bath. — This consists of a circular rack for 



test-tubes within a water-bath. It is sometimes employed instead 



of the steam cylinder for sterilising nutrient jelly in tubes, by 



boiling for an hour for three successive days. 



Hot-water Filter. — A copper 

 funnel with double walls, the inter- 

 space between which is iilled with 

 hot water. A glass funnel fits in- 

 side the copper cone, the stem of 

 the glass funnel passing through 

 and being tightly gripped by a per- 

 forated caoutchouc plug, which fits 

 in the opening at the apex of the 

 cone. The water in the cone is 

 heated by applying the flame of a 

 burner to a tabular prolongation 

 of the water-chamber. In a more 

 recent model, as represented in 

 Fig. 31, this prolongation is dis- 

 pensed with, and the temperature is 

 maintained by means of a circular 

 burner which acts at the same time 

 as a funnel ring. In Rohrbeck's 

 model the funnel of the filter is 

 connected with a flask, from which 



the test-tubes can be easily filled with the hquid jelly (Fig. 253). 

 Glass Vessels. — A number of glass vessels should be kept in 



stock according to requirements. 



Bohemian hard glass flasks are employed in several sizes, for 



boiling nutrient media. The conical forms are especially used in the 



larger sizes for storing nutrient jelly. 



Glass funnels, large and small, are necessary, not only in the 



processes of preparing nutrient jelly, but for filtering solutions of 



aniline dyes and for general purposes. 



Fig. 253. — HoT-w.iTER Filteking 

 Appaeatus with Ring Burner. 



I 



