240 METAMORPHOSIS OF TISSUE. 



the blood of the carnivora, and which are only very slightly increased 

 or replaced by the food of such animals, should be sufficient to 

 adapt the materials of respiration for oxidation. We shall revert 

 to the alkaline carbonates and phosphates when we enter upon the 

 more special consideration of the processes of nutrition and 

 secretion. 



In treating generally of the distribution of chloride of sodium 

 in the animal organism (vol. i, pp. 430-436), we drew attention to 

 the well-established fact that the quantity of this salt varies very 

 slightly in most of the animal juices, especially in the blood, and 

 is restricted within tolerably narrow limits for each class of 

 animals, being wholly independent of the nature of the food and 

 of the quantity of this substance taken up with the food (see vol. i, 

 p. 431, and vol. ii, p. 189) ; we have also found that the quantity 

 of salt in the excretions, and more especially in the urine, corre- 

 sponds very closely with the quantity in the food, whilst direct 

 experiments have shown that this salt when it is injected into the 

 blood, is rapidly excreted through the salivary glands, the mucous 

 membranes, and the kidneys. We think that these well-established 

 facts give great probability to the idea that this substance is 

 necessary for the animal vital process. Even if we attach little 

 weight to the instinct which leads certain domesticated animals 

 eagerly to lick up the salt placed before them, and induces the 

 natives of certain districts where salt is scarce to barter slaves and 

 gold-dust for this substance, yet certain experiments on the 

 quantity of salt contained in the blood, together with Boussingault's 

 investigations,* sufficiently show that the use of salt with the 

 ordinary food is an indispensable requisite towards the healthy 

 condition of domesticated animals. Boussingault instituted experi- 

 ments on two lots of oxen (each consisting of three), one of which he 

 fed for a month on food with which salt had been mixed, and the 

 other on fodder containing no salt, and found by accurate weighing 

 that the salt produced no effect upon the formation of the flesh and 

 fat, or on the quantity of milk, but that towards the close of the 

 period of observation the external appearance and activity of the 

 animals which were being fed upon food to which salt had been added 

 were very superior to that of the animals which were fed without 

 salt, for the latter presented a less smooth and shining coat, while 

 their hair was matted and in part fell off; their gait was alsoheavy, 

 and they exhibited a cold temperament. The utility of common 



* Ann. de Chim. et de Phys. 3m e Se'r. T. 19, pp. 117-125, et T. 22, p. 110; 

 or Compt. rend. T. 25, p. 729. 



