CHANGES IX INTESTINES. THE FECES. 



and some are found in secondary products formed by bacterial 

 or chemical action. Some of the molecular combinations are 

 large, while others are relatively small. No conclusion, there- 

 fore, as to the weight of the nitrogenous bodies can be drawn 

 from the nitrogen found, but the datum has value from other 

 standpoints. 



Total Nitrogen. The total nitrogen in the feces may be accurately de- 

 termined by a combustion process, but most readily by the Kjeldahl proc- 

 ess which is now everywhere employed. This depends on the conversion 

 of the nitrogen into ammonia by prolonged heating with sulphuric acid to 

 which a very little metallic mercury is added. Often a mixture of pure 

 sulphuric acid and potassium sulphate is employed. At the end of the 

 digestion the mixture is made alkaline with a slight excess of ammonia- 

 free sodium hydroxide and distilled. The ammonia formed is collected in 

 standard acid and measured in this by titration of the excess of acid with 

 standard alkali. 



Even in condition approaching starvation, when no food 

 proteins can possibly be present, the feces always show some 

 nitrogen, which, as pointed out above, must come from the 

 secretions thrown into the intestines and from the remains of 

 bacteria and their products. A part of this nitrogen there- 

 fore has once been absorbed to be later thrown back into the 

 intestine, which fact must be kept in mind in making deduc- 

 tions from the nitrogen found as to the loss of nitrogen in 

 assimilation. Although usually overlooked the nitrogen ex- 

 isting in the bacterial cells is an appreciable quantity and often 

 makes up a good fraction of the whole. It has recently been 

 shown that in normal feces nearly one-third of the dry weight 

 may often be made up of the bacteria. 



The amount of nitrogen excreted increases with the food 

 consumed in general, and especially if this food contains a 

 large amount of indigestible substance. The nitrogen of a 

 meat diet is always more completely utilized than is the nitro- 

 gen of beans, for example, where there is considerable cellu- 

 lose to disintegrate. The nitrogen in this case is largely in 

 the form of protein residues, and may be detected as will be 

 pointed out below. In pathological conditions of the diges- 



