COLT/VATION OF ANAEROBIC BACTERIA. 77 



taken with a sterilised platinum wire, and the con- 

 tents of the test-tube are inoculated with it, a puncture 

 being quickly made right down to the bottom of the 

 tube. The cotton-wool plug is then replaced, and an 

 india-rubber cap drawn over it, or better, the upper 

 end of the tube is immersed in fluid paraflBn. All 

 kinds of bacteria, anaerobes, aerobes and facultative 

 anaerobes, develop equally well in these tubes, only 

 the appearances of the cultures vary considerably 

 according to their need of oxygen. The strictly 

 anaerobic bacteria develop only in the lower part of 

 the tube, whilst in the upper part, as far as the oxygen 

 of the air can penetrate into the nutrient medium, a 

 more or less broad band of gelatine or agar-agar 

 remains free. The more strictly anaerobic a bacterium 

 is, the deeper down does its development commence. 

 Facultative anaerobes on the other hand flourish both 

 in the upper and lower layers, or even on the surface 

 of the medium, and we can measure their need of 

 oxygen very well by their position in these cultures. 

 Strictly aerobic species, which of course do not occpr 

 in the hydrogen tubes, would grow only on the surface 

 of these cultures, there being no sign of growth along 

 the whole length of the puncture. This method there- 

 fore affords us an excellent means of determining 

 which of the colonies which have developed in the 

 coated tube are really anaerobic. 



This cultivation in deep layers is to be recommended. 



