488 OF FOOD, AND THE DIGESTIVE PROCESS. 



hard parts, that form the skeletons of the Invertebrata. To these ingredients 

 we may also add Iron, which is -a very important element in the red blood of 

 Vertebrated animals. These substances are contained, more or less abund- 

 antly, in most articles generally used as food ; and where they are deficient, 

 the animal sufFers in consequence, if they are not supplied in any other way. 

 Thus common Salt exists, in no inconsiderable quantity, in the flesh and 

 fluids of animals, in milk, and in the egg : it is not so abundant, however, in 

 plants ; and the deficiency is usually supplied to herbivorous animals by some 

 other means. Thus salt is purposely 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 the yolk and white 

 of the Egg, and in Milk, the substances on which the young animal subsists 

 during the period of its most rapid growth ; and it abounds, not only in many 

 animal substances used as food, but also (in the state of phosphate of lime or 

 bone-earth) in the seeds of -many plants, especially the grasses. In smaller 

 quantities it is found in the ashes of almost every plant. When flesh, bread, 

 fruit, and husks of grain, are used as the chief articles of food, more phosphorus 

 is taken into the body than it requires ; and the excess has to be carried out in 

 the excretions. Sulphur is derived alike from vegetable and animal substances. 

 It exists in flesh, eggs, and milk ; also in the azotized compounds of plants ; 

 and (in the form of sulphate of lime) in most of the river and spring-water that 

 we drink. Iron is found in the yolk of egg, and in milk, as well as in animal 

 flesh; it also exists in small quantities in most vegetable substances used as 

 food by Man, such as potatoes, cabbage, peas, cucumbers, mustard, &c. ; 

 and probably in most articles, from which other animals derive their support. 

 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. It 

 is most commonly taken in, among the higher animals, combined with Phos- 

 phoric acid ; and in this state it exists largely in the seeds of most grasses, 

 especially in wheat flour. If it were not for their deficiency in Phosphate 

 of lime, some of the Leguminous seeds would be more nutritious than wheaten 

 flour ; the proportion of azotized matter they contain being greater. A con- 

 siderable quantity of lime exists, in the state of carbonate and sulphate, in all 

 hard water. 



649. The absolute quantity of food, required for the maintenance of the 

 Human body in health, varies so much with the age, sex, and constitution 

 of the individual, and with the circumstances in which he may be placed, 

 that it would be absurd to attempt to fix any standard which should apply to 

 every particular case. The appetite is the only sure guide for the supply of 

 the wants of each ; but its indications must not be misinterpreted. To eat 

 when we are hungry, is an evidently natural disposition; but to eat as long 

 as we are hungry, may not always be prudent. Since the feeling of hunger 

 does not depend so much upon the state of fulness or emptiness of the sto- 

 mach, as upon the condition of the general system, it appears evident that the 

 ingestion of food cannot at once produce the effect of dissipating it, though 

 it will do so after a short time ; so that, if we eat with undue rapidity, we 

 may continue swallowing food long after we have taken as much as will really 

 be required for the wants of the system ; and every superfluous particle is 

 not merely useless, but injurious. Hence, besides its other important ends, 

 the process of thorough mastication is important, as prolonging the meal, 

 and giving time to the system to become acquainted (as it were) that the sup- 

 ply of its wants is in progress ; so that its demand may be abated in due time 

 to prevent the ingestion of more than is required. It is very justly remarked 

 by Dr. Beaumont, that the cessation of this demand, rather than the positive 



