GENERAL MORPHOLOGY AND PHYSIOLOGY. 137 



compounds in the medium in which they grow. 

 Pasteur divided bacteria into two great classes, 

 the aerobic and anaerobic ; and considered that the 

 latter not only had no need for oxygen, but that its 

 presence was actually deleterious. Though this 

 view must be considerably modified, the terms are 

 convenient, and are still retained. They are well 

 illustrated by the bacillus of anthrax, and the 

 bacillus of malignant oedema ; and a simple plan of 

 demonstration has been employed by the author. 

 A fragment of tissue from the spleen, for example, 



FIG. 64. FIG. 65. 



VIBRIOS IN WATER CONTAMINATED SPIRILLUM UNDULA, 



WITH SEWAGE, x 1200. x 1200. 



known to contain anthrax bacilli, is deposited with 

 a sterilised inoculating needle, with the necessary 

 precautions, on the surface of nutrient agar-agar 

 in a test-tube ; another tube of nutrient agar-agar 

 is liquefied, and when cooled down almost to the 

 point of gelatinisation, a part is poured into the 

 first tube, so that when it sets the piece of tissue 

 is completely embedded. A piece of tissue from 

 an animal suffering from malignant oedema is 

 treated in the same way, and the tubes are 

 placed in the incubator. If then we examine 



