334 PRACTICAL PHYSIOLOGY 



of strong hydrochloric acid causes separation out of the fatty acids. 

 The presence of phosphorus in this emulsion can also be deter- 

 mined. 



Nervous tissue (brain) which has been previously dried serves as an 

 excellent source for lipoid material. A rough separation may be 

 carried out by first extracting the material with cold acetone which 

 takes out the cholesterol, then with cold ether which removes mainly 

 phosphatides (do P. test) and finally with hot alcohol or chloroform 

 which extracts the cerebrosides. Test last extract for presence of a 

 reducing sugar galactose (see p. 215). 



Pulses: Determine presence of a native protein. 



Pea flour, 10-20 gms., is stirred up with twice its weight of 10 per 

 cent. NaCl solution and allowed to stand for at least one hour. The 

 starch is then filtered off and the filtrate saturated with ammonium 

 sulphate. The precipitate which results is a mixture of two globulins, 

 legumin and vicilin. These may be separated from their solution in 

 very dilute ammonium sulphate, as legumin is precipitated on T 6 o 

 saturation with ammonium sulphate (i.e. addition of 150 c.c. saturated 

 ammonium sulphate solution to 100 c.c. of the globulin solution). The 

 ammonium sulphate can be got rid of from the precipitate by dialysis. 

 Prove globulin nature of legumin. 



The table on following page gives a summary of the composition of 

 some of the chief foodstuffs. The data have been taken from the recent 

 analyses of R. H. A. Plimmer (Analyses and Energy Value of Foods, H.M. 

 Stationery Office, 1921). 



The Methods for the Estimation of General Metabolism. In carrying 

 out the examination of the changes which take place in the organism, 

 whether the subject be starving or fed, there are three lines of attack. 

 Obviously if all three methods can be used at once the results obtained 

 are most comprehensive. The three lines of attack are the investiga- 

 tion of the excreta (urine and faeces), the respiratory exchange by way 

 of the lungs, and the heat loss. The direct determination of heat 

 loss may be ruled out at once as a practicable method as it involves the 

 construction of a most costly calorimeter. The other two channels of 

 excretion fortunately enable us to determine very accurately the energy 

 exchange by indirect methods. 



The study of the composition of the urine, particularly the relation 

 of the output of nitrogen to the intake in the food, is essential. When 

 great exactitude is required the output of total nitrogen in the faeces 

 must also be determined. A small amount of nitrogen is also excreted 

 in the sweat, also by the loss and growth of epithelial structures, but as a 

 general rule this loss is neglected. Since the average protein contains 

 approximately 16 per cent, of nitrogen each gramme of nitrogen excreted 

 corresponds to 6-25 gms. of protein. 



The end products of the metabolism of fats and carbohydrates under 

 normal conditions are water and carbon dioxide. As it is technically 

 very difficult to estimate water-gain and loss the gaseous component 

 is selected. We can, it is true, gain a good deal of information about 

 the changes in metabolism by the study of the carbon dioxide output, 

 but if we wish the fullest possible information about the nature of the 

 changes, not merely the combustion, but the energy output, we must also 

 determine at the same time the oxygen consumption. 



This combined method is carried out most easily by the use of the 

 Douglas bag, where by means of a mouthpiece or face mask with two 



