TEXT-BOOK OF BACTERIOLOGY. 73 



be mentioned. Pasteur's consists of one part of tartrate of ammo- 

 nium, ten parts of sugar candy, and the ashes of one part of yeast, 

 with 100 parts of water. 



Cohn's consists of i gram of phosphate of potassium, | gram of 

 basic triple phosphate of lime, and 100 grams of water. To the 

 whole is added 1 gram of tartrate of ammonium. 



But it was soon observed that it was better to breed the bacteria 

 under conditions resembling those of their natural state as closely 

 as possible. 



Therefore, for the purely saprophytic species, which occur 

 principally on vegetable substances, infusions of wheat, pea-straw, 

 potatoes, and decoctions of fruit were prepared ; the species ob- 

 served in animal excrements were to thrive on extracts of manure, 

 etc. For the benefit of those whose habitat is the living organism, 

 efforts were made to produce a liquid that should approximatelj' 

 answer to the juices of the body without being too complicated in 

 its composition. It was to contain liquid albumin and extractives 

 in about the same quantities as they occur in the blood, and were 

 to show a decided alkaline reaction. 



The simplest and most satisfactory medium in. most cases was 

 found to be a decoction of chopped meat, made slightly alkaline by 

 an addition of solution of soda. Thus Pasteur early emploj'ed his 

 bouillon of fowl's flesh with success, and we still often employ it, or 

 at least a similar liquid food, at the present day. 



We prepare our bouillon according to Loffler's directions. We 

 take a definite quantity (500 grams) of finely-minced beef, as lean 

 as possible, and mix it up with about a litre of ordinary water and 

 allow the mixture to stand about twelve hours. In summer this 

 should take place in the refrigerator to prevent putrefaction. A 

 number of soluble albuminous and extractive substances pass into 

 the liquid part, which is then separated from the flesh. This is 

 best done by turning out the whole mass into a looselj'-woven 

 cloth ("cheese-cloth") and squeezing with the hands until the 1,500 

 grams of mixture have yielded 1,000 grams of meat extract. 



If this liquid be heated, most of the albuminous substapces con- 

 tained in it are precipitated and lost. To make good this loss and 

 to insure the food solution as much albuminous matter as possible, 

 we previously add a certain quantity of peptone, which cannot coag- 

 ulate in the warming process. We take about 1^ for the quantity 

 above mentioned — therefore about 10 grams — and to facilitate the 

 solution of the peptone we add i^ or 5 grams of common salt. 



The meat extract, with the peptone and the salt, is next boiled 

 for about three-quarters of an hour in the water bath over the open 



