CH. in.] VESSELS, ETC., USED IN CULTIVATIONS. 27 



chamber for several hours (three to six) to a temperature of 

 from 130 to 150 C. : while hot they are taken out seriatim, 

 plugged with the sterile cotton-wool, and replaced in the air- 

 chamber, and heated again for several hours. All this, and 

 other operations to be described below, may appear to some 

 rather tedious and unnecessarily complicated, but it cannot 

 be too strongly insisted on that in these matters one cannot 



FIG. 4. HOT-AIR CHAMBER FOR STERILISING TEST-TUBES AND COTTON-WOOL. 



An iron chamber with double wall, the inner chamber having separate folding 

 doors. In the inner chamber are placed the test-tubes, glasses, &c., and the 

 cotton-wool, the latter in a loose condition. Both sets of doors are closed, and 

 the apparatus heated by a large Fletcher's burner. A thermometer passing from 

 the inner chamber through the upper wall indicates the temperature of the chamber. 



be too scrupulous. A slight relaxation may, and occasionally 

 is, followed by disastrous consequences in the shape of 

 accidental contamination, and consequent loss of material 

 prepared at the cost of much labour and time. Long 

 experience in these matters has taught me that, although in 

 some instances less scrupulous care has not been followed 



