38 MICRO-ORGANISMS IN WATER 



In inoculating from one tube to another, both are 

 held in the left hand in a downward position, the one 

 between the thumb and first finger, the other between 

 the first and second fingers ; the stoppers are removed 

 and carefully held between the fingers also of the left 

 hand (one between the third and fourth, the other 

 between the fourth and fifth), and a minute trace of the 

 old cultivation is transferred on the point of the needle 

 to the fresh tube. In the case of agar-agar tubes, in 

 which a certain amount of liquid is present, or in the 

 case of bouillon and other fluid media, the tubes must 

 be held in as inclined a position as possible without 

 allowing any liquid to run up the tubes within reach 

 of the cotton-wool plugs. In inoculating potatoes, the 

 platinum-needle carrying the living material is streaked 

 over the surface of the potato, whilst the cover is very 

 cautiously lifted at one side, if the latter is contained 

 in a dish ; whilst in potato tube-cultures the mode of 

 procedure is similar to that already described above for 

 the inoculation of test-tubes. 



Anaerobic cultivations. — As some organisms, like 

 the bacilli of tetanus and malignant oedema, have the 

 remarkable property of being unable to grow in the 

 presence of free oxygen, special contrivances have to be 

 introduced for their cultivation and study. A number 

 of devices have been from time to time employed for 

 this purpose, but we shall only describe those which 

 we have found of most general utility. 



The following method is admirably adapted for 

 obtaining colonies of anaerobic micro-organisms as well 

 as generally for carrying out experiments on the efiect 

 of different gases on bacterial life : — 



Larger test-tubes (commonly known as ' boihng- 

 tubes') are charged with about 20 c.c. of gelatine- 

 peptone apiece, plugged with cotton-wool and sterilised 



