148 SCIENCE PROGRESS. 



should contain as much of the cheap carbohydrates and as 

 little of the dear proteid as possible. 



6. The non-nitrogenous food-stuffs are only oxidised 

 when the amount of proteid given at the same time is in- 

 sufficient for the animal's total requirements. 



7. To increase the amount of meat on an animal, the 

 proteid given in the food must exceed the indispensable 

 minimum. 



CIRCULATING PROTEID. 



If an animal be starved, the daily excretion of urea 

 sinks rapidly for the first few days, and then for a con- 

 siderable time remains very nearly constant. It might be 

 thought that if, during this time, an amount of proteid were 

 given to the animal, containing a proportion of nitrogen 

 equivalent to that which the starving animal was excreting, 

 the loss of nitrogen to the body would be checked, the loss 

 of nitrogen in the urine being replaced in the tissues by 

 the nitrogen of the food. This is, however, not the case. 

 After the administration of proteid to the starving animal, 

 the quantity of urea excreted is almost doubled, showing 

 that nearly the whole of the proteid taken in is disintegrated 

 within twenty-four hours, and excreted with the urine. In 

 order to produce a condition of nitrogenous equilibrium, it 

 is necessary to give the animal two and a half times the 

 amount of proteid corresponding to the nitrogen that is 

 excreted during- starvation. Voit has explained this fact by 

 supposing that the proteid taken in with the food has a 

 twofold destination in the body, part of it going to supply 

 the tissue-waste, and being built up into the living proto- 

 plasm of the tissues (' morphotic ' or 'tissue proteid'), 

 while the other and greater moiety ('circulating proteid') 

 passes into the juices that bathe the protoplasmic elements 

 of the cells, and is rapidly broken up and oxidised there, 

 without at any time forming an integral part of the proto- 

 plasm. 



This teaching of Voit has been subjected to searching 

 criticism by P Auger (6). He shows, in the first place, that 



