406 MANUAL OF PHYSIOLOGY. 



gives rise to the gravest symptoms called u ramie poisoning, which 

 closely coincide with those observed in experimental annihilation 

 of the renal function. 



From the foregoing it would appear to be satisfactorily settled 

 that the urea, which is by far the most important ingredient of 

 the secretion of the kidney, is probably made elsewhere and not 

 in that organ, whose duty seems to be chiefly to remove it from 

 the blood. This is most probably also true of all the other organic 

 constituents of the urine. The question then arises : Where is the 

 urea formed? 



We naturally turn for an answer to the most wide-spread and 

 most actively changing nitrogenous tissue, namely muscle. Here, 

 however, we find no response, for neither does muscle contain 

 much urea, nor does any very active muscular work perceptibly 

 increase the general urea elimination. In muscle, however, a 

 material closely allied to and readily convertible into urea, namely 

 kreatin, occurs, and it has been suggested that this substance is 

 changed into urea in the kidney. This cannot explain the origin 

 of all the urea which appears in the urine, for, as already remarked, 

 the urea excretion does not correspond with the muscle meta- 

 bolism. 



Without for one moment doubting that some, probably a con- 

 siderable quantity of urea comes from muscle, which forms so 

 large a part of our bodies, we conclude that there must be and 

 assuredly are many other sources of urea, as there are many other 

 parts or organs where nitrogenous textures are undergoing chem- 

 ical changes and gradual waste. 



One source of urea the liver, is specially worthy of note, since 

 it helps to explain the striking relation between the amount of 

 albuminous food and the quantity of urea eliminated, the latter 

 following immediately and running parallel with the former. 

 There can be no doubt that most people consume much more al- 

 buminous food than is necessary for the adequate nutrition and 

 preservation of the nitrogenous tissues, and therefore must have 

 a surplus of nitrogenous material in their bodies. It may be re- 

 membered, as was pointed out in the chapter on digestion, that in 

 all parts of the alimentary tract there is a limit to the absorption 



