io BIOLOGICAL PROBLEMS 



tuberculosis had any relation to the amount of protein 

 taken. It was clearly related to a low calorie value, 

 and especially to absence of a due proportion of fat. 



The question of the so-called "specific dynamic 

 action" of protein is a difficult one. The fact to 

 which this imposing name is given is this. Suppose 

 that the energy given off by an individual is being 

 measured by conversion into heat, and that a known 

 calorie value of fat or carbohydrate is taken and the 

 extra energy output determined. It is found to be 

 equivalent to that of the food taken. This is not 

 so with protein. In this case more energy is given 

 out than corresponds to that of the food taken ; the 

 chemical processes of the cells have been stimulated 

 to greater activity, and the protein taken has brought 

 about the combustion of other material in addition to 

 that of itself. There is, as yet, some dispute as to 

 whether this is of real advantage to the organism or 

 not. There are two statements with respect to it that 

 make it difficult to believe that it is other than waste- 

 ful. It is produced at a particular time after the 

 ingestion of protein, whether wanted at that time or 

 not. And, secondly, it is said to show itself only as 

 heat. Hence my remark above as to protein being in 

 some circumstances a heat-giving food. At the same 

 time the meaning of this statement is not quite clear. 

 Presumably it is that the energy produced by the 

 extra combustion is given off when not required for 

 other purposes, and is therefore wasted in the form of 

 heat. In other words, it must be got rid of somehow. 

 But, of course, if the body is burning up material to 

 keep up its temperature in cold weather the extra heat 

 is not wasted, since it takes the place of other oxida- 

 tions. 



We may remember that in the process of utilization 

 of protein for energy purposes the nitrogenous part is 



