320 THE HUMAN BODY. 



centage of oxygen in them is much higher, there being 

 one atom of oxygen for every two of hydrogen in their 

 molecule. 



Inorganic Foods. Water; common salt; and the chlo- 

 rides, phosphates, and sulphates of potassium, magnesium 

 and calcium. More or less of these bodies, or the materials 

 for their formation, exists in all ordinary articles of diet, so 

 that we do not swallow them in a separate form. Phosphates, 

 for example, exist in nearly all animal and vegetable foods; 

 while other foods, as casein, contain phosphorus in combina- 

 tions which in the Body yield it up to be oxidized to form 

 phosphoric acid. The same is true of sulphates, which are 

 partially swallowed as such in various articles of diet, and are 

 partly formed in the Body by the oxidation of the sulphur of 

 various proteids. Calcium salts are abundant in bread, and 

 are also found in many drinking-waters. Water and table- 

 salt form exceptions to the rule that inorganic bodies are 

 eaten imperceptibly along with other things, since the Body 

 loses more of each daily than is usually supplied in that way. 

 It has, however, been maintained that salt, as such, is an 

 unnecessary luxury; and there seems some evidence that 

 certain savage tribes live without more than they get in the 

 meat and vegetables they eat. Such tribes are, however, 

 said to suffer especially from intestinal parasites; and there 

 is no doubt that to civilized man the absence of salt is a great 

 privation. 



Calcium seems to be an essential constituent of all living 

 cells and in some way closely connected with the manifestation 

 of their activity. As previously mentioned the heart of a 

 frog after thorough irrigation with dilute solution of sodium 

 chloride ceases to beat, but resumes its pulsations when a 

 minute trace of calcium chloride is added to the solution; 

 and while ordinary serum restores the beat of such a washed- 

 out heart, serum from which all its calcium has been removed 

 does not. Moreover if defibrinated blood to which a little 

 more sodium oxalate than is sufficient to precipitate all its 

 calcium has been added, be circulated through the vessels of a 

 muscle, the latter loses, its contractility, apparently because 

 the slight excess of oxalate precipitates the calcium of the 

 muscle-fibres; for the contractility may be restored by sup- 

 plying some dissolved calcium chloride. Nerves treated simi- 

 larly lose their irritability"; and the eggs of some aquatic 



