CULTIVATION OF ANAEROBIC BACTERIA. 75 



If agar- agar should be used for these cultures, the 

 experiments must be performed as quickly as possible, 

 as this nutrient medium solidifies very quickly, and 

 cannot be reliquefied like gelatine, for, as has already 

 been mentioned, it only liquefies at a temperature very 

 nearly that of boiling water, at which most bacteria 

 are killed. The test-tube containing the agar-agar may, 

 during the passage of the hydrogen, remain in the 

 air, but it is better to place it in a large vessel of water 

 at about 42° C, so that it may not cool down too 

 quickly. The gas is then allowed to pass briskly 

 for about three minutes, after which the tubings are 

 melted oS", and the test-tube rolled in the air, or on 

 water of from 20° to 25° C. 



It is advisable to add to the nutrient media, used in 

 these experiments, as a rule gelatine or agar-agar, 

 some substance which has a great affinity for oxygen. 

 Chemically pure grape sugar is most suitable for this 

 purpose, having the great advantage over other 

 reducing agents which might be used (such as, for 

 example, sodium or calcium formate), that it helps the 

 agar-agar to adhere to the sides of the test-tube, and 

 not to fall off even during long experiments, as alone 

 it very frequently does. On this account, when 

 cultivations of anaerobes are to be made, 1 °/ oi 

 chemically pure grape sugar is added to the gelatine 

 or agar-agar preparations. As, however, the use of 

 grape sugar is not injurious, but rather, as a rule. 



