FURTHER BIOCHEMICAL METHODS vi,,-5 



is a constant volume type in which the reaction flask is attaclied to a 

 U-shaped manomctric tube. The change in pressure on the Hquid in 

 the tube is read, from which the Oi-uptakc and CO2 evolved are 

 easily calculated. Anacrobically, CO2 and II 2 arc readily deter- 

 mined. The manual by Dixon (1934) may be consulted for theoretical 

 and manipulative details. 



Cleavage of Carbohydrates, Alcohols, and Glucosides 



Under this heading in Leaflet V are given the most common rou- 

 tine tests, designed merely to show whether or not an organism pro- 

 duces acid or gas in certain standard media. Such tests are valuable, 

 but do not give a sufficient idea as to the action of the organism on the 

 carbon compound under investigation. In a comprehensive physiologi- 

 cal study, various more detailed methods are necessary. The present 

 leaflet is designed to indicate a few of these methods. 



Choice of Carbon Compounds. The carbon compounds employed in a 

 study of this sort should be of the utmost purity. A considerable 

 variety of such compounds is now available. It is not always necessary 

 to use all of them; but for many groups of bacteria it will be known in 

 advance which may be expected to give the most useful information. 

 The following list gives the compounds most frequently used in fer- 

 mentation studies: 



Monosaccharides: Pentoses: 1-arabinose, xylose, rhamnose 



Hexoses: glucose, fructose, mannose, galactose 

 Disaccharides: Sucrose, maltose, lactose, trehalose, cellobiose, melibiose 

 Trisaccharides: Raffinose, melezitose 

 Polysaccharides: Starch, inulin, dextrin, glycogen 

 Alcohols : Trihydric : glycerol 



Tetrahydric: erythritol 



Pentahydric: adonitol, arabitol 



Hexahydric: mannitol, dulcitol, sorbitol 

 Glucosides : Salicin, coniferin, aesculin 



Several of these compounds are hydrolyzed or otherwise decom- 

 posed at the temperature necessary for sterilization. For careful 

 work, therefore, such compounds must be sterilized separately, by 

 Berkefeld filtration or by autoclaving in concentrated (ordinarily 

 20%, unless the viscosity is too great), slightly acid (pll().8) aqueous 

 solution, and added aseptically to the basal medium. In the latter 

 case, autoclaving for 15 minutes at 15 pounds pressure and plunging 

 into cold water has proved useful. Sugars are particularly subject to 

 chemical change in the presence of phosphates or in alkaline solution. 



Ordinarily a concentration of 1% in the medium is satisfactory; 

 but one can often economize (in the case of expensive compounds) by 

 employing low'er concentrations. 



Choice of a Basal Medium. There are many bacteria that will not 

 grow in beef extract agar or broth, and modifications are necessary in 

 order to secure sufficient urowth to determine whether or not utiliza- 



