TEST-TUBE CULTIVATIONS. 7 I 



Examination of test-tube cultivations. 



The appearances produced by the growths in test- 

 tubes can be in most cases sufficiently examined 

 with the naked eye. The illustrations in the ac- 

 companying plates (Plates II., III., IV., V., VIII., 

 XIII., XIV., XXIV.) are given as examples of the 

 various changes produced in the nutrient media. 

 In some cases the jelly is partially or completely 

 liquefied, while in others it remains solid. The 

 growths may be abundant or scanty, coloured or 

 colourless. The nutrient jelly may itself be tinged 

 or stained with products resulting from the growth 

 of the organisms. When liquefaction slowly takes 

 place in the needle track, or the organism grows 

 without producing this change, the appearances 

 which result are often very delicate, and in some 

 cases very characteristic. The appearance of a 

 simple white thread, of a central thread with 

 branching transverse filaments, of a cloudiness, or 

 of a string of beads in the track of the needle, may 

 be given as examples. In such cases much may be 

 learnt by examining the growth with a magnifying 

 glass. Here, however, a difficulty is encountered, 

 for the cylindrical form of the tube so distorts the 

 appearance of its contents, that the examination is 

 rendered somewhat difficult. To obviate this, the 

 following very simple contrivance may be employed 

 with advantage. 



Cheshire's Trough. This consists of a rect- 

 angular vessel, four inches in height, two inches in 



