13 MICRO-ORGANISMS AND DISEASE. [CHAP. 



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 by bad results, still I 

 have had also many unpleasant failures owing to slight laxity 

 in these matters. 



F IO . 4. HOT-AIR CHAMBER FOB STERILISING TEST-TUSKS 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, &e . , 

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

 closed, and the apparatus heated by a large Fletcher's burner. A thermo- 

 meter passing from the inner chamber through the upper wall indicates the 

 temperature of the chamber. 



Several weeks' work may be annihilated by a single 

 omission. Sometimes one is perhaps in a slight hurry, and 

 does not think the want of an additional heating of the test- 

 tube or cotton-wool or an additional boiling of the fluid will 

 be followed by any bad consequences. But, alas, nature does 

 not take into account our convenience, and failure is our 

 reward. If in any kind of experiments " overdoing " is an 

 error in the right direction, it is in these very experiments in 

 the cultivation of micro-organisms. 



