80 LABORATORY EXERCISES IN BACTERIOLOGY. 



experience of bacteriologists in this direction, that much can be done in selective cultiva- 

 tion by substituting the proteids of other animals, even from man. The development of 

 this field presents possibilities for investigation. The albumins at present utilized are 

 for the most part of the nature of albumoses, peptones, and serum albumin ; and their 

 preparation is largely empiric, and the precise composition of the products a matter of 

 uncertainty. The amount of albuminous substance in ordinary bouillon and its deriva- 

 tives is in reality much less than was originally contemplated in its manufacture ; and it 

 is probable that the many complex organic and inorganic salines and derivatives pre- 

 served in its manufacture constitute the most important feature of the substance. One 

 sees but little difference practically, for example, in the cultural qualities of the media 

 made from the commercial beef extracts and those made from the fresh beef ; yet it is 

 well known that these extracts contain comparatively little of the meat albumins and 

 are largely composed of the various salines and extractives. In blood-serum, of course, 

 the albumin of the serum is preserved ; and this substance more nearly than the bouillon 

 preparations represents a natural proteid medium. In bouillon preparations the loss 

 of the albumins is sought to be corrected by the addition of commercial peptones (really 

 albumose for the most part) ; and solutions of the latter will be found to possess every 

 practical value of the more complexly arranged bouillon. 



i. Bouillon. Bouillon is the nutrient medium commonly selected when large, 

 massive cultures of bacteria are required to be grown, or when it is desired to have 

 the bacteria in liquid surroundings, to facilitate observations as to their power of 

 movement, their intimate relations, or their chemical activities; or when they are 

 intended for animal inoculation. It is prepared either from the fresh meat or from 

 the commercial beef extracts. It is very much more convenient to make the prepara- 

 tion from the latter, and so far as the value of the product as a nutrient medium is 

 concerned, it is apparently in no way less advantageous than that made from the 

 fresh meat. It possesses one important advantage, moreover, in that it is less likely 

 to contain the meat sugars uniformly met in the meat bouillon, rendering it preferable 

 in exercises intended to demonstrate reaction changes and gas formation by bacteria ; 

 and in its manufacture it is more easy to maintain a definite and uniform composi- 

 tion. 



(a) When making bouillon from the fresh beef, the meat is obtained from the 

 butcher as fresh as possible ; it should be free from fat and should be finely chopped 

 or ground. The meat pulp thus procured is soaked over night in water (preferably 

 boiled water in proportion of 500 grams of the pulp to 1000 cubic centimeters of 

 water), being kept in the refrigerator in order to prevent the development of the bac- 

 teria present in the meat. The following morning the red meat infusion is strained 

 off through a piece of cheese-cloth, the pulp being compressed if necessary to obtain 

 a full liter of the liquid. If less than a liter be obtainable, it is customary to add 

 water to make up the amount to this quantity. The infusion is next heated moder- 

 ately (between 50 and 60 C.) in a suitable vessel (as a granite-ware stew-pan), and 

 ten grams of dried peptone and five grams of sodium chloride are added, and with con- 

 stant stirring with a clean glass rod, thoroughly mixed and dissolved in the warm infu- 

 sion. When the peptone and salt are dissolved, the preparation is boiled sharply, with 

 constant stirring, until all the albumins coagulable by heat are separated and the liquid 

 is of a clear, amber color. It is then filtered through paper; and should the filtrate 

 be at all turbid, it should be reboiled and again filtered. The filtrate is now cooled 

 to room temperature and the amount corrected to one liter, after which it is titered 

 with decinormal sodium hydroxide solution and the reaction adjusted. It is again 



