CHAPTER III. 



VESSELS AND INSTRUMENTS USED IN CULTIVATIONS. 



ALL vessels (flasks, test-tubes, beakers, filters, calico) to be 

 used are first thoroughly sterilised by overheating. In the 

 case of flasks and test-tubes, this can be done by exposing 

 them thoroughly in all parts to the open flame of a large 

 Fletcher's burner ; while thoroughly heated the mouth is 

 plugged with a good long plug (i to 2 inches) of sterile 

 cotton-wool, this being pushed in by means of overheated 

 forceps. The plug in all cases must not be loose, but also 

 not too firm an error in the latter direction being of course 

 preferable to one in the former. The cotton-wool plug may, 

 if long enough, be single ; or, if short ones are used, double. 

 Or the flasks and test-tubes are placed in an air-chamber 

 (see Fig. 4) heated by a large Fletcher's burner for several 

 hours, up to between 130 and 150 C. In the case of small 

 flasks and test-tubes this process is of course much more 

 convenient, since a large number can be heated simul- 

 taneously. Beakers and glass filters to be used merely for a 

 temporary operation are placed over a wire net on a tripod 

 and heated by the flame of a Bunsen's burner. In the case 

 of test-tubes which are to receive cultivation-fluids, I generally 

 expose them, after having been cleaned and dried, in the air- 



