288 BACTERIA. 



by keeping the plates on which the nutrient medium 

 was spread in an atmosphere of hydrogen. When puncture 

 inoculations are made in tubes of gelatine to which grape 

 sugar has been added, there is no growth along the part 

 of the track of the needle near the surface, but in the 

 deeper part away from the air, there is a moderately 

 luxuriant growth which appears in the form of a central 



f 



Specimen from pure culture of the Tetanus Bacillus, with enlarged 

 spore-bearing " drum-stick " ends. X 1000. 



streak, from which numerous spikes pass laterally into 

 the surrounding medium. The culture at this stage has 

 very much the appearance of a spruce-fir, the lower branches 

 (*.<?., those in the deeper part of the gelatine where the 

 access of oxygen to the organism is entirely cut off) 

 being longer and more distinctly marked than those nearer 

 the surface. Later this characteristic appearance is lost, 

 the organism invades the whole of the nutrient medium, 



