PHYSIOLOGICAL AVAILABILITY. 835 



the combustion heat of the feces and urine with the same diet, there is 

 obtained the net calorific value of the diet. This value, calculated in 

 percentage of the total energy content of the food, is called the physio- 

 logical availability by RuBNER. 1 In order to elucidate this we will give 

 a few of RUBNER'S values. The loss in calories, as well as the physio- 

 logical availability, is calculated in percentages of the total energy 

 content of the food. 



In order to simplify the calculation of the energy exchange there exists, besides 

 the above-mentioned standard figures for the physiological calorific value of the 

 organic foodstuffs, also for the carbon of the carbon dioxide, and for the oxygen 

 other standard factors. Thus for 1 gram of meat (dry substance) free from fat 

 and extractives we have the calculated value of 5.44-5.77 calories. KOHLER 2 

 found 5.678 calories for 1 gram of ash and fat-free dried-meat substance of the 

 ox and 5.599 calories for horse meat. According to FRENTZEL and SCHREUER 3 

 45.4 calories is calculated for 1 gram of nitrogen in fat and ash-free dried-meat 

 feces (dog), while 6.97 to 7.45 calories is calculated for 1 gram of nitrogen in meat- 



urine. The calorific urine quotient - ^ seems still, as above given, not to be 



constant for human beings, but is dependent upon the variety of food. 



Instead of the direct determination the heat of combustion can also be deter- 

 mined from the elementary composition acording to the following principle as 

 suggested by E. VoiT. 4 If we designate the heat of combustion for 1 gram of the 

 substance by calories and the quantity of oxygen necessary for the complete com- 

 bustion of 1 gram of the substance ( = oxygen capacity of the substance) by 0, 



then ^r -=K, which is the combustion value for 1 gram of oxygen. The 



oxygen capacity can be calculated from the elementary composition, and when 

 the value of K is known, the combustion heat of a chemical compound or a known 

 mixture can be readily determined. The value K is almost constant for substances 

 of the same groups; but also different groups show among themselves only slight 

 deviation for this value. VOIT obtained the following values for a few of the food- 

 stuffs : 



K (in kg. Calories.) O Capacity. 



Plant protein ................................ 3 . 298 1 . 740 



Animal protein ............................... 3 . 273 1 . 741 



Fat ......................................... 3.271 2.863 



Carbohydrate ................................ 3 . 525 1 . 156 



These methods of calculation are, according to VOIT and KRUMMACHER, 

 admissible for practical purposes. 



1 Zeitschr. f. Biologic, 42. 



2 Zeitschr. f. physiol. Chem., 31. 



3 The works of Frentzel and Schreuer may be found in Arch. f. (Anat. u.) Physiol., 

 1901, 1902, and 1903. 



4 Zeitschr. f . Biologie, 44. See also Krummacher. ibid. 



