422 



EXCRETION. 



with the exact proportion and condition of all the principles of this class contained in 

 the urine. In all the processes of nutrition, it is found that the inorganic constituents of 

 the hlood and tissues accompany the organic matters in their various transformations, 

 although they are themselves unchanged. In fact, the condition of union of the inorganic 

 with the organic principles is so intimate, that they cannot be completely separated with- 

 out incineration. In view of these facts, it is evident that a certain part, at least, of the 

 inorganic salts of the urine is derived from the tissues, of which, in combination with 

 organic matters, they have formed a constituent part. As the kidneys frequently elimi- 

 nate from the blood foreign matters taken into the system and are capable sometimes of 

 throwing off an excess of the normal principles which may be introduced into the cir- 

 culation, it can be readily understood how a large proportion of some of the inorganic 

 matters of the urine may be derived from the food. 



From the fact that the inorganic matters discharged in the urine are generally the 

 same as those introduced with the food, and that they vary in proportion with the con- 

 stitution of the food, it is difficult to ascertain how far their presence and quantity in the 

 urine represent the processes of disassimilation. One thing, however, is certain : that 

 the organic constituents of the food, the blood, the tissues, and the urine, are never with- 

 out inorganic matter in considerable variety ; and it is more than probable that the pres- 

 ence of these salts in a tolerably definite proportion influences the processes of absorption 

 and secretion and has an important bearing upon nutrition ; but we are as yet so imper- 

 fectly acquainted with the processes of nutrition of the tissues, that we cannot follow 

 out all the relations of the inorganic matters, first to nutrition, and afterward to disas- 

 similation. 



Chlorides. Almost all of the chlorine in the urine is in the form of chloride of so- 

 dium, the amount of chloride of potassium being insignificant and not of any special 



physiological importance. It is unnecessary, in 

 this connection, to describe the well-known 

 properties of common salt, and the methods for 

 determining its presence and proportion in the 

 urine are fully treated of in works upon physi- 

 ological chemistry. All that we have to con- 

 sider is its importance and significance as a uri- 

 nary constituent. 



By reference to the table of the composition 

 of the urine, it is seen that the proportion of 

 chloride of sodium is subject to very great vari- 

 ations, the range being from three to eight parts 

 per thousand. This at once suggests the idea 

 that the quantity excreted is dependent to a 

 considerable extent upon the amount taken in 

 with the food ; and, indeed, it has been shown 

 by numerous observations that this is the fact. 

 The proportion of chloride of sodium in the blood 

 seems to be tolerably constant; and any excess that maybe introduced is thrown off 

 chiefly by the kidneys. It has been shown conclusively that deprivation of common salt 

 in the food after a time is followed by serious disturbances in the general process of 

 nutrition ; and it is an acknowledged fact that this proximate principle is a constituent 

 of every tissue of the body, except the enamel of the teeth. As the chlorides are de- 

 posited with the organic matter in all the acts of nutrition, they are found to be elimi- 

 nated constantly with the products of disassimilation of the nitrogenized parts, and their 

 absence from the food does not completely arrest their discharge in the urine. Accord- 

 ing to Robin, by suppressing salt in the food, its daily excretion may be reduced to from 



FIG. 128. Crystals of chloride of sodium. 

 (Funke.) 



