492 G. H. DREW. 



IV. Peptone Calcium Acetate Medium. 



Calcium acetate (Ca(CH3COO)2) ... 5-0 grammes 



Peptone (Witte's) 0*2 



Potassium nitrate (KNO3) ..... 0*5 ,, 



Sea-water 1000-0 c.c. 



The fluid media II, III, and IV were also made up with the addition 

 of 0"2 grammes of Magnesium tartrate per 1000 c.c. 



The fluid media were made up in 1500 c.c. resistance glass flasks, 

 and 1000 c.c. of medium was used for each culture. 



For other purposes a simple solution of Peptone in sea-water was 

 employed (2 grammes to 1000 c.c), and media were also used con- 

 sisting of this Peptone solution with the addition of 0*5% of various 

 carbohydrates, such as Cane sugar. Dextrose, Laevulose, Mannite, 

 Lactose, etc., with sufficient Neutral Ked solution to colour them, in 

 order to test the acid-forming properties of the bacteria in the 

 presence of Carbohydrates. 



The ordinary "Koch" steam sterilizer, and an iron oven for dry- 

 heat sterilization, were used, and gasoline cooking stoves were found 

 to be the most satisfactory source of heat. It was found an advantage 

 to use Petri dishes with porous earthenware covers, which enabled the 

 water of condensation to evaporate partially ; the evaporation could 

 be checked at any time by covering the dishes with a bell-jar lined 

 with wet filter-paper. It was usually found necessary to keep all 

 cultures on tables with their feet standing in dishes of paraffin oil, in 

 order to prevent the attacks of ants and other insects. In all other 

 respects ordinary bacteriological routine was followed, and the methods 

 need not be further particularized here. 



The reduction of the Nitrate to a Nitrite in fluid culture media was 

 tested for by the addition of 5 c.c. of 10% Sulphuric Acid and 2 c.c. of 

 a 1% solution of Metaphenylene diamine hydrochloride to 25 c.c. of 

 the culture. The production of a brown colouration (due to the 

 formation of Bismarck Brown) is an indication of the presence of a 

 Nitrite, and is an extremely delicate reaction. 



The Diphenylamine and Brucine sulphate reactions were also used 

 when testing for the presence of Nitrates. 



The formation of Ammonia was tested for by the addition of 5 c.c. 

 of 10% Potassium hydrate and 5 c.c. of Nessler's Eeagent ; the white 

 precipitate formed on the addition of the Potassium hydrate does not 

 appreciably interfere with the test, though it renders it less delicate. 



Under expeditionary conditions, and in the absence of the somewhat 



