METABOLISM, NUTRITION AND DIETETICS 525 



honey proteins are present ; and even when bees fed on pure 

 honey or sugar manufacture wax, it may be derived from the 

 broken-down proteins of their own bodies. 



(2) From Protein. Dry protein contains on the average 16 per 

 cent, of nitrogen and 50 per cent, of carbon, and urea contains 

 46 per cent, of nitrogen and 20 per cent, of carbon. Urea is 

 therefore three times as rich in nitrogen as the protein from 

 which it is derived, but two and a half times poorer in carbon ; 

 and less than one-seventh of the carbon of protein will be 

 eliminated in the urea, which carries off all the nitrogen. A 

 carbonaceous residue is left, which, it is extremely probable, may 

 under certain circumstances be converted into fat, as we know 

 it may into carbo-hydrate ; yet absolutely flawless experiments 

 to prove the direct production of fat from protein seem still to 

 be wanting. 



In the experiments of Bauer, the amount of oxygen consumed 

 and of carbon dioxide and nitrogen excreted was determined in 

 starving dogs. Phosphorus, which, as is well known, causes 

 extensive fatty changes in the organs, was then administered in 

 small doses for several days. The excretion of nitrogen was doubled, 

 the excretion of carbon dioxide and the consumption of oxygen 

 diminished to one-half. When the animals died, in a few days, the 

 organs were all found loaded with fat. In one case 42^4 per cent, of 

 the solids of the muscles and 30 per cent, of the solids of the liver 

 consisted of fat. This is much more than the normal amount. It 

 was assumed that the fat could not have been simply transferred 

 from the adipose tissue, since the dog had been starved for twelve 

 days before the phosphorus was given, and died on the twentieth 

 day of starvation. Now, after such a period of hunger the amount 

 of fat in the adipose tissue is greatly reduced. It was therefore 

 concluded that the source of the fat could only have been the 

 broken-down protein. Since the nitrogen excretion was increased, 

 while the carbon excretion was diminished, it was supposed that a 

 residue rich in carbon must have been split off from the proteins, 

 and, remaining unburnt in the body, must have been converted 

 into fat. Experiments of this kind are open to criticism on several 

 grounds, but especially on this : that unless the fat-content of the 

 whole body before the administration of the poison is known, it is 

 impossible to be sure that the fat in a particular tissue has not been 

 increased simply by the transportation of fat from some other tissue. 

 It has been conclusively shown that migration of pre-formed fat 

 does occur, and on an extensive scale, in phosphorus poisoning. 

 For example, a dog was fed for a time with sheep's tallow, and fat 

 was laid down in its adipose tissue with the physical and chemical 

 characters, not of dog's, but of sheep's fat. The animal was then 

 poisoned with phosphorus, and the fat which accumulated in the 

 liver examined. It also resembled sheep's fat, as it should have 

 done had it migrated from the adipose tissue, and not dog's fat, 

 as it might have been expected to do had it been formed in the 

 hepatic cells from protein. The ease with which connective-tissue 

 fat i.e., food fat migrates to the liver suggests, with other facts, 

 that the liver has a special relation to the transformation o this 



