38 INTRODUCTION. 



upon nutrition. They indicate a certain deficiency in the 

 nutrition of animals deprived of it, but not any considerable 

 loss of weight. Before these observations were made, Dailly 

 made upon twenty sheep analogous experiments, which were 

 continued for three months. At the end of that time the 

 lot which received salt presented a considerable excess of 

 weight (about 22f Ibs.) over the others. 1 



It is a significant fact that the quantity of chloride of so- 

 dium existing in the blood is not subject to variation, but 

 that an excess introduced with the food is thrown off by the 

 kidneys. The quantity in the urine, then,' bears a relation to 

 the quantity introduced as food, but the proportion in the 

 blood is constant. This is another fact in favor of the view 

 that the presence of a definite quantity of common salt in 

 the circulating fluid is essential to the proper performance of 

 the general function of nutrition. 



Origin and Discharge of Chloride of Sodium,. This 

 substance is always introduced with food in the condition 

 in which it is found in the body. It is contained in the sub- 

 stance of all kinds of food, animal and vegetable ; but in the 

 herbivora and in man, this source is not sufficient to supply 

 the wants of the system, and it is introduced, therefore, as 

 salt. The quantity which is discharged from the body has 

 been estimated by Barral 2 to be somewhat less than the 

 quantity introduced, about one-fifth disappearing ; but these 

 estimates are not exactly accurate, for the amount thrown off 

 in perspiration has never been directly ascertained. It exists 

 in the blood in connection with the phosphate of potassa, and 

 a certain amount is lost in a double decomposition which 

 takes place between these two salts, resulting in the forma- 

 tion of chloride of potassium and phosphate of soda. It also 

 is supposed to furnish the soda to all the salts which have a 



1 LONGET, Traite de Physiologic, tome i., p. 76. 



3 Cited by ROBIN and VERDEIL. Chimie Anatomique et Physiologique, Paris, 

 1853, tome ii., p. 103. 



