348 LECTURE XV. 



The figures show that the number of calories in each case were about the 

 same in the three experiments. If such experiments are carried out 

 unaccompanied by muscular work, the difference between the effect of 

 albumin, on the one hand, and that of the carbohydrates and fats, on the 

 other, towards the entire metabolism, becomes more marked. 



We have now finished all that we care to say with regard to the mutual 

 relations existing among the three most important organic nutrients. 

 We have discussed two ways in which they may replace one another. On 

 the one hand, it is possible by means of a chemical transformation for one 

 nutrient to be converted into another, and, again, the replacement may 

 be merely one of calorific values, without any such transformation being 

 necessary. The latter method of one food replacing another is undoubtedly 

 of the greatest importance in the whole economy of metabolism. It 

 represents the greatest possible utilization of the available energy, and 

 guarantees the satisfactory maintenance of the entire metabolism, even 

 when one of the nutrients is not momentarily available. Albumin is an 

 exception. It is only in part replaceable. If the organism is starving, 

 it tries to preserve its albumin by consuming first the fats and car- 

 bohydrates available, thus protecting its tissues against severe injury. 

 The former condition of the body is therefore quickly regained as soon as 

 food is eaten again. It is only when the organism draws upon its own 

 protein for the main supply of the required energy, that the end is near. 

 It is of great interest to note, that the reserve materials held in store by 

 the organism, and drawn upon during starvation, likewise enter into metab- 

 olism strictly in accordance with their calorific values. As soon as the 

 body substances are called upon to act as combustible material, they also 

 follow the Law of Isodynamics. 



