304 



IMPORTANCE OF MINEEAL MATTEE 



and chlorides of calcium and magnesium. These substances are there- 

 fore essential constituents of food. 



2. As necessary for digestive, respiratory and other processes. The 

 blood contains iron ; the saliva, gastric juice and other secretions con- 

 tain potassium. Chlorine and hydrochloric acid are essential ingredients 

 in the gastric juice ; the thyroid gland contains iodine. 



Consider first the substances required for the formation and renewal 

 of bone. The largest and most important mineral constituents are 

 phosphoric acid and lime. In normal bone, these are present in the 

 proportions of one molecule of phosphorus pentoxide (P 2 O 5 ) to three 

 molecules of lime (CaO), i.e., 142 to 168 by weight ; but as some of 

 the lime of bones is also present as carbonate in bone ash, the pro- 

 portions by weight are generally about 1 of phosphorus pentoxide to 

 1*5 of lime. It would seem reasonable, therefore, to expect that the 

 food of an animal, in order to serve for the nutrition of bone, should 

 contain phosphorus pentoxide and lime in about this ratio. 



So, too, cows' milk, which we may assume to be particularly 

 adapted for the requirements of a young animal, contains the two 

 above-mentioned constituents in approximately equal proportions by 

 weight, while common salt is also present in about the same amount. 



Since phosphorus is also required for the formation of other tissues, 

 e.g., the brain, we may conclude that the ideal food of an animal should 

 contain about equal proportions of lime and phosphorus pentoxide. 



Now, in England, the above considerations have perhaps not often 

 much importance, because of the variety of food given to horses and 

 cattle ; but in South Africa, where oat hay i.e., oats cut just before 

 they are ripe, and dried forms the sole food of many horses and mules, 

 sometimes supplemented by a few mealies (i.e., maize grain), they 

 become, in the author's opinion, of great importance. 



Now, in the seeds of most plants there is much more phosphorus 

 pentoxide than lime, while the proportions vary very much in the 

 foliage of different plants. 



In the following table are given the ratios of phosphorus pentoxide 

 to lime present in many foodstuffs, from the analyses of Wolff and 

 Warington : 



CaO. 

 4-78 

 4-45 

 3-60 

 2-55 

 1-81 

 0-16 

 0-77 

 0-62 

 0-44 

 0-04 



Cereals are thus remarkable for the preponderance of phosphorus 

 pentoxide over lime which they contain. Thus, while it is probable 

 that in the whole food of an animal the phosphorus pentoxide ought 

 not to exceed the lime, it is evident that in the usual South African 



