ADVANCED PHYSIOLOGICAL CHEMISTRY 475 



are two subdivisions of the subject; the one called, general metabolism, 

 has to do with the building up or breaking down of the tissues. It 

 derives its information from a comparison of the amount of the various 

 food stuffs absorbed, with the amount of their excretory products. 

 The other, called special metabolism, has to do with the exact chemical 

 changes which absorbed food stuffs undergo, and the localisation of 

 the actual organ or organs in which the various changes are effected. 



Space will only permit us to indicate some of the methods employed 

 in studying general metabolism, and to describe briefly how the results 

 obtained may be interpreted. The actual methods of analysis have 

 already been fully described in the previous chapters, and in the 

 following description reference will be made to the pages on which the 

 most suitable method for each determination can be found. 



General Metabolism. In order to study this a balance sheet must 

 be drawn up, on one side of which is placed the intake (the amount of 

 food and oxygen absorbed), and on the other the output (the amount of 

 the various bodies excreted in the urine, faeces, breath, and sweat). 



I. The Intake. The value of a diet can be expressed either as 

 its chemical value, or as its physical value. The chemical value means 

 the amount of proteid, fat, carbohydrate, and salt which it contains. 

 This is determined by referring to analytical tables of the various food 

 stuffs (especially serviceable for this purpose are the tables of Konig. 

 The amount of the various food stuffs administered can then be 

 easily determined by multiplying the percentage given on the tables 

 by the amount of food given. When it is desired to be specially 

 accurate an actual analysis of the food is necessary, and when the 

 metabolism of proteid is being specially studied, it is customary to 

 determine the amount of nitrogen which the food stuff contains 

 (Kjeldahl's method, p 243), and this multiplied by 6'3 gives the 

 amount of proteid. 



The physiological heat value of a diet means the number of calories 

 which it can yield during its metabolism in the body. To find the 

 total heat value of the diet, all that is necessary is to multiply the 

 physiological heat values of the administered food stuffs by the amount 

 of each which the diet contains. 



The Form in which the Food Stuffs are best given for Metabolism 

 Experiments. Proteid. This is usually given as meat, from which all 

 the visible fat and tendon are, as far as possible, removed. When 

 calculating the amount of proteid from the nitrogen present, the 

 gelatin and extractives which the meat contains may be neglected, for 

 gelatin, in the presence of an excess of proteid, has the same metabolic 

 value as native proteids, and the extractives exert no influence on the 



