NECESSARY MATERIALS OF ANIMAL FOOD. 251 



aids in preventing the decomposition of the organic constituents of these 

 fluids. ^Phosphorus has been supposed, until recently, to be chiefly re- 

 quisite as one of the materials of the nervous tissue ( 383) ; and also, 

 when acidified by oxygen, to unite with lime in forming the bone-earth 

 by which bone is consolidated. But there is reason to believe, from the 

 results of late inquiries, that the acid and alkaline phosphate of lime and / 

 soda are very important constituents of the various fluid secretions, and / 

 have a large share in their respective actions. Sulphur exists in smalf" "N. 

 quantities in several animal tissues ; but its part appears to be by no 

 means so important as that performed by Phosphorus. Lime is required 

 for the consolidation of the bones, and for the production of the shells / 



and other hard, parts that form the skeletons of the Invertebrata ; and / 



also as the base of the acid phosphate, which has been just referred to / 

 as an important constituent of the animal fluids. Lastly, Iron is an 

 essential constituent of Haematosine ; and is consequently required for 

 the production of the red corpuscles of the blood in Vertebrated animals? J^ 



439. These substances are contained, more or less abundantly, in 

 most of the articles generally used as food ; and where they are defi- \ 

 cient, the animal suffers in consequence, if they be not supplied in any 

 other way. Thus common Salt exists, in no inconsiderable amount, in the 

 flesh and fluids of animals, in the milk, and in the substance of the egg ; 



it is not so abundant, however, in Plants ; and the deficiency is usually 

 supplied to herbivorous animals in some other way. Thus, salt is pur- 

 posely mingled with the food of domesticated animals ; and in most 

 parts of the world inhabited by wild cattle, there are spots where it 

 exists in the soil, and to which they resort to obtain it. Such are the 

 "buffalo-licks" of North America. Phosphorus exists also, in combi- 

 nation with proteine-compounds, in all animal substances composed of 

 these ; and in the state of phosphate, combined with lime, magnesia, and 

 soda, it exists largely in many vegetable substances ordinarily used as 

 food. The phosphate of lime is particularly abundant in the seeds of 

 the grasses ; and it also exists largely, in combination with caseine, in 

 Milk. Sulphur is derived alike from vegetable and animal substances. 

 It exists, in union with proteine-compounds, in flesh, eggs, and milk ; 

 also in several vegetable substances ; and, in the form of sulphate of 

 lime, in most of the river and spring water that we drink. 



440. Lime is one of the most universally diffused of all mineral 

 bodies ; for there are very few Animal or Vegetable substances in which 

 it does not exist. The principal forms in which it is an element of Ani- 

 mal nutrition, are the carbonate and phosphate. 'Both these are found 

 in the ashes of the grasses, and of other plants used as food ; the phos- 

 phate of lime being particularly abundant (as already mentioned) in the 

 corn-grains. The production of these cannot take place, to their fullest 

 extent, unless the soil previously contain phosphate of lime in a state in 

 which the plant can receive it; and it is now understood, that the 

 diminished fertility of many lands is due, in great part, to the exhaus- 

 tion of the soil as regards this ingredient. The restoration of the alka- 

 line and earthy phosphates to the soil, in the form of manure, is the 

 obvious means of preserving its fertility ; but so long as a very large 

 proportion of the excrements of animals (the materials of which are 

 originally derived from the earth, through the vegetables it supplies) is 



