INORGANIC SUBSTANCES. 45 



twice its usual proportion of carbonic acid ; and the other alkaline salts 

 have a similar dissolving action upon this gas. The blood as it circu- 

 lates among the tissues absorbs from them the carbonic acid formed in 

 their substance, and carries it away to be eliminated by the lungs. If 

 this important property, which depends upon the alkalescence of the 

 blood, be lost by its neutralization, the elimination of carbonic acid by 

 the lungs is no longer possible, and the tissues become overloaded by 

 its accumulation. This is probably the cause of death in Bernard's 

 experiment. 



The alkalescence of the blood-plasma is due in great measure to the 

 alkaline phosphates, which are present in human blood in the proportion 

 of 0.67 per thousand parts. A peculiar relation exists in this respect, 

 for different classes of animals, between the alkaline phosphates and the 

 alkaline carbonates, which are to be mentioned hereafter. Both these 

 groups of salts have, in solution, an alkaline reaction ; and both con- 

 tribute to the alkalescence of the blood in man and animals. But in the 

 carnivorous animals it is the phosphates which preponderate, while in 

 the herbivora the carbonates are more abundant. In species fed upon 

 both animal and vegetable food the two kinds of salts are present in 

 nearly equal proportion ; and in the same animal either the phosphates 

 or the carbonates may be made to predominate by increasing the pro- 

 portion of animal or vegetable food respectively. This is due to the 

 fact that muscular flesh is comparatively abundant in phosphates, while 

 vegetable matters abound in salts of the organic acids, which give rise 

 by their decomposition in the system to carbonates of the same bases. 



The alkaline phosphates are mainly derived from the food. They 

 circulate with the animal fluids, and are finally excreted under their own 

 form in the perspiration, the mucus, and the urine. A partial exception 

 to this rule is found in the urine, where a portion of the alkaline sodium 

 phosphate is replaced by the acid biphosphate, giving to the whole fluid 

 an acid reaction. The explanation of this change, as generally under- 

 stood, is the following. A nitrogenous organic acid of new formation, 

 namely, uric acid, makes its appearance in the system, and is excreted 

 by the urine, in the form of a neutral combination, as sodium urate. 

 It is believed to combine, at the time of its formation, with a portion 

 of the sodium of the sodium phosphate, and the remainder of this salt 

 is thus converted into a biphosphate. The normal reaction of the urine 

 is therefore really due to the formation in the body of an acid substance ; 

 although the substance so produced does not appear in the urine as the 

 immediate cause of its acidity. 



There is also evidence that a certain amount of phosphoric acid is 

 formed in the body by the process of oxidation. A substance containing 

 phosphorus in organic combination, known as "lecithine," exists in 

 various parts of the system, especially in the blood, brain, and nerves, 

 and is also taken with certain kinds of food ; but no such substance is 

 met with in the excreted fluids, where phosphorus exists only in the 

 form of the phosphatic salts. It is no doubt oxidized in the internal 



