USES OF THE GASES OF THE BLOOD. 713 



being found in all growing tissues; as is well known, they are espe- 

 cially deposited, as a consolidating material essential to the formation 

 of the skeleton, and of the dentine and enamel of the teeth. Of these 

 tissues, although the enamel undergoes no nutritive change after it has 

 been formed, and the dentine very little, the bones are constantly ex- 

 hibiting very active metamorphoses. Carbonate of lime, phosphate of 

 magnesia, and silicates and fluorides, are usually associated with the 

 phosphate of lime. 



But there are other salts, such as the phosphates and sulphates, both 

 of potash and soda, which, probably, are derived from the oxidation of 

 the phosphorus and sulphur contained in the phosphorized fatty mat- 

 ters found in the red corpuscles, and especially in the nervous tissues, 

 and in the sulphuretted albuminoid substances existing in muscle and 

 brain. The phosphorus and sulphur in these compounds, are either 

 directly oxidized and combined with soda or potash, or else they pass 

 first into intermediate substances, such as the highly sulphuretted 

 substance, the taurin of the bile. If carbonates of soda or potash 

 exist in the blood, they also are probably not nutrient, but represent 

 the results of chemical retrogressive metamorphoses in the blood and 

 tissues. Moreover, the phosphate of soda, which has an alkaline re- 

 action, and any carbonate of soda which may be present in the blood, 

 serve very important and special uses in that fluid, helping to dissolve 

 the albumen, to favor the chemical oxidation of many substances in 

 the blood, the absorption of gases, and the passage of the nutrient 

 plasma through the walls of the capillaries. The salts of potash are, 

 it would seem, absolutely necessary to the nutritive changes which 

 occur in muscular tissue. The importance of potash especially, in 

 preserving the healthy condition of the blood, perhaps by determining 

 or aiding the chemical actions necessary for that end, is illustrated in 

 the beneficial effects of fresh vegetables and fruits, as articles of food. 

 They especially abound in neutral or acid salts of potash; and a diet 

 from which they are absent, if long used, induces that condition of 

 the blood, which causes scurvy or scorbutus. The employment of 

 neutral salts of potash, aids, at least, in the cure of this disease; but it 

 is more effectually remedied by the use of lime-juice, potatoes, or fresh 

 vegetables themselves. Hence, perhaps, a vegetable diet operates on 

 the blood and tissues, in some other mode than by the potash in which 

 it abounds. 



Of the gases contained in the blood, the nitrogen is probably indif- 

 ferent, and without special office, its relative proportion constantly 

 varying, both in arterial and venous blood. On the other hand, the 

 oxygen must be regarded as an agent of the highest importance. It 

 purifies the blood, and, dissolved in, or combined with, the cruorin of 

 the red corpuscles, is by them carried through the system, and oper- 

 ates on all the tissues. Its action is not so much to contribute to the 

 formation of tissue, by being combined with, or fixed in, the tissues in 

 the act of morphosis, as to stimulate the tissue elements, especially 

 those of the nervous and muscular tissues, to their proper functions, 

 causing chemical changes or oxidations of their substance, or of the 

 blood passing through them, essential to their action, and more or less 



