INORGANIC CELL-CONSTITUENTS. 135 



phate than those of the carnivora. The combination 2(P0 4 )Mg"H 4 is 

 often found in the urine of the herbivora when fed on grain, and is 

 occasional!}' met with in intestinal concretions under the same conditions. 

 Its origin, physiological importance, and mode of disposition in the body 

 is apparently identical with that of the alkaline phosphates. Occasion- 

 ally magnesium phosphate undergoes crystallization, as in the urine of 

 the rabbit and in suckling calves. 



10. SODIUM AND POTASSIUM SULPHATES (S0 4 K 2 , S0 4 Na 2 ). These 

 salts are to be regarded as normal constituents in small amount of most 

 of the animal fluids and tissues. They are not, however, found in the 

 milk, bile, or gastric juice, their presence in the ash being without impor- 

 tance, since in incineration of sulphurous organic compounds the sul- 

 phuric acid, liberated in this process, unites with the carbonates and 

 alkaline bases. A certain amount of these salts is held in solution in the 

 blood and in the urine, though the}' are less abundant than either the 

 chlorides, phosphates, or carbonates. When present in the animal body 

 they are in the form of solution. Only part of the sulphates found in 

 the animal body is derived from without, since it is possible that 

 through the oxidation of sulphur of organic compounds sulphuric acid is 

 formed, which leaves the body united with alkaline bases. These salts 

 are excreted from the body through the urine, where a greater part of the 

 sulphuric acid is not derived from the sulphates contained in the food, 

 but through the internal oxidation of sulphur-holding compounds. This 

 is especially shown by the fact that an abundant animal diet increases 

 the amount of sulphates in the urine hand in hand with the increase of 

 urea, while a vegetable diet decreases it. The sulphates partly con- 

 tribute to the acid reaction of the urine of carnivora. 



The entire quantity of sulphur in the body of an adult man has been 

 estimated at about one hundred and ten grammes, and to keep this 

 amount constant at least one gramme must be taken daily in the food, 

 where it is combined with albuminoids. A part of this sulphur passes 

 into the hair and nails, part is consumed in the manufacture of various 

 complex, sulphur-holding compounds, such as taurin, taurocholic acid, 

 gelatin, chondrin, mucin, etc., while part is eliminated in the form of 

 sulphates. 



11. HYDROCHLORIC ACID (HC1). The presence of free hydrochloric 

 acid has as yet only been shown to exist in the case of gastric juice of 

 mammals. Its origin and importance will be considered under the sub- 

 ject of Gastric Juice. 



Oxygen, nitrogen, and carbon dioxide are also constant constituents 

 of animal fluids and tissues, and their importance will be discussed under 

 the subject of Respiration. 



A few other inorganic substances have been found as more or less 



