!58 BACTERIOLOGICAL EXAMINATION OF WATER. 



None of these varieties were pathogenic to mice or pigeons, 

 The spores were not destroyed by exposure to current steam for 

 five or six hours. Also specimens of earth, after drying in an 

 oven for four or five months, produced distinct growths when 

 planted out on potato. The optimum temperature of the 

 thermophylic bacteria appeared to be between 60 and 70 C. 

 Macfadyen and Blaxall, in their later experiments with ther- 

 mophylic bacteria, employed salt potato-agar as a means of 

 isolating the different varieties of these organisms. They found 

 that the colonies of the bacteria remained discrete on this 

 medium, so it was possible to obtain readily pure cultures of 

 the organisms. "The potato-agar is prepared as follows: 

 Potatoes are first steamed, peeled, and pounded. To 100 

 grammes of potato is added one litre of tap-water, and the 

 mass is steamed for half an hour and filtered. To the filtrate 

 1*5 to 2 per cent, of agar is added, and the whole autoclaved 

 for fifteen minutes. It was found an advantage to add 1 per 

 cent, of salt. After neutralisation with soda, and further 

 steaming, the potato-agar is filtered into test-tubes and 

 sterilised once more." From the primary colonies on the salt 

 potato-agar sub-cultures were made on the ordinary culture 

 media. The various organisms were found to stain with 

 ordinary dyes, but, on the whole, carbol-methylene blue gave 

 the best results. It was usually found advisable before staining 

 to treat the cover-slip preparation with dilute acetic acid ; this 

 cleared away a zooglcea-like membrane, which often interfered 

 with clear staining. Macfadyen and Blaxall described fourteen 

 thermophylic bacteria. 



Bacillus I. Was isolated from animal dejecta, and produced 

 colonies on agar closely resembling those of the B. anthracis. 

 It liquefied gelatine on the fourteenth day. There was no 

 growth on potato, and no action was produced in milk. In 

 broth there was a viscous deposit, and the supernatant broth 

 was clear. It gave no indol reaction. It was a large, non- 

 motile bacillus, which did not stain with Gram, and contained 

 a spore towards the centre of the slightly swollen rod. 



Bacillus II. Also isolated from animal dejecta, produced 

 dull, white, round, smooth colonies. In broth there was a 

 deposit and a slight surface film; indol reaction was obtained. 



