THE MINERAL SALTS 9 



to the amount of phosphorus in the casein " in order to find 

 the quantity of phosphoric acid which is present in the milk 

 as such." 



It is doubtful, however, whether the argument can be 

 properly extended to the P 2 O 5 in this way. There is good 

 reason to believe that the phosphorus in casein is already 

 fully oxidised, i.e. that it is present as P 2 O 5 ; and if that be 

 so, one is prompted to ask, why not deduct the CaO which 

 also occurs as a constituent of the casein in the original 

 milk? 



There can be no question as to the condition as regards 

 oxidation of the sodium and potassium compounds in 

 natural organic matter. These elements occur in the soil 

 chiefly as oxysalts and chlorides, and, as such, are taken up 

 by plants. These compounds may undergo various changes 

 in plants and animals, but they are probably not reduced. 

 The same argument applies also, with more or less force, to 

 the calcium and magnesium compounds. 



Functions of the Ash Ingredients. It is very difficult 

 to determine precisely what functions some of the ingredients 

 of the ash perform in the living organism. In other cases it 

 is more or less readily apparent. 



The presence of sodium chloride in plants appears to be 

 purely accidental. The great majority of plants grow as well, 

 and some of them better, in the total absence of this sub- 

 stance. Cattle and sheep, and most other animals, exhibit 

 a strong desire for common salt. When opportunity offers, 

 they will lick it as a child sucks sugar. Salt is frequently 

 mixed with their food as a condiment; it improves their 

 appetites, aids digestion, and appears to be beneficial to 

 their health, but in what way is not known with certainty. 

 It has been argued that a certain amount of common salt 

 is necessary as a source of the hydrochloric acid which is 

 found in the stomach and which promotes the process of 

 peptic digestion. It is probable, however, that the chlorides 

 naturally present in the food of herbivora are sufficient to 

 provide all the hydrochloric acid required. 



Potassium compounds are essential for the growth of 



