350 



PHYSIOLOGY 



CHAP. 



given, but never in proportion with it. Meconium and the faeces of 

 fasting consist exclusively in the residues of the secretions poured 

 into the intestine, which contain certain metabolites that are 

 excreted neither by the kidneys nor by the skin and lungs. But 

 even on a strict flesh diet the faeces have, as a rule, the same 

 composition, a minimal amount of alimentary residues only being 

 visible under the microscope. 



If sugar, starch, ,and fat be added to the flesh diet, the residues 

 of these substances appear in the faeces only when they are 

 administered in large quantities. So that on this mixed diet also, 

 the faeces consist mainly of the waste products of the digestive 

 secretions. It is only on feeding with certain foods that are very 

 rich in starch, e.g. bread and potato, that the faeces are found to 

 contain alimentary residues (for the most part little altered) along 

 with a reduced amount of metabolites. 



These results were extensively confirmed in Voit's laboratory 

 by Fr. Miiller and Kieder (1882). This last author estimated the 

 amount of nitrogen found daily in the faeces and urine of both 

 dogs and man, on a diet entirely or almost entirely free from 

 nitrogenous substances ; and obtained results which induced him 

 to think it probable that not only in the dog but in man also 

 the faeces consist mainly of katabolic products, excreted by the 

 digestive organs. In fact, from three series of experiments on a 

 man fed on this regimen, he obtained the averages shown in the 

 following table : 



So that on a non-nitrogenous diet a man (weighing about 70 

 kilos.) excretes a daily average in the faeces of 0'73 grm. nitrogen 

 (an amount not much in excess of that excreted by a dog of 35 

 kilos., which on an average equals 0'64 grm.). This amount of 

 nitrogen represents about 8 per cent of the total nitrogen 

 eliminated by the body. 



During an abundant mixed diet, man excretes on an average 

 2*53 grms. nitrogen in the faeces (Pettenkofer and Voit). Of this 

 nitrogen it is probable that 1*80 grms., i.e. 71 per cent, comes from 

 alimentary residues, and that 0'73 grm., i.e. 29 per cent, must be 

 referred to katabolic residues excreted by the intestinal canal. In 

 this case, therefore, the amount of alimentary residues in the faeces 



