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 (1 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 simultaneously. 

 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-chamber 

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

 130 150 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 be too 

 scrupulous. A slight relaxation may, and occasionally is, 







