HUMAN PHYSIOLOGY. 



H 



UMAN PHYSIOLOGY is the science which 

 treats of the functions of the body and the 

 manner in which these are performed. By a 

 function we mean the action performed by any 

 part of the body. For example, one of the 

 functions of the liver is to secrete bile, while 

 that of the stomach is to digest food. It is 

 the object of the present paper to describe as 

 briefly as is compatible with clearness the most 

 important of these functions. The functions of 

 the human body may be conveniently classified 

 into three great divisions : i. The Function of 

 Nutrition, or the nourishment of every part of the 

 body, so as to enable each part to perform its 

 special function ; 2. The Function of Innervation, or 

 the actions performed by the nerves, spinal cord, 

 and brain ; and 3. The Function of Reproduction, 

 or the perpetuation of the species by offspring. 



I. THE FUNCTION OF NUTRITION. 



This function is a complex process. To keep 

 up the integrity and vigour of the body, food 

 must be procured, chewed or masticated, mixed 

 with saliva, swallowed, digested in the stomach, the 

 nutritious material absorbed by special organs in 

 the bowels, called villi, and from them carried 

 to various glands, where it is elaborated into 

 blood. The blood is then conveyed through 

 the body, giving up to the tissues what they require 

 for nourishment, and carrying away materials 

 resulting from their decay. Thus rendered im- 

 pure, the blood must have the noxious materials 

 removed. For this purpose, several organs, such 

 as the lungs, the liver, the skin, the kidneys, and 

 the lower bowel, are set apart. Thus the blood 

 is constantly replenished with nutritious matters, 

 and constantly being purified, so as to fit it for 

 supplying each individual particle or cell of the 

 body with exactly the material it requires. Bone 

 requires earthy salts, muscle requires albumen, 

 the nervous system requires fat, and so on. 



The process of nutrition is complex only in the 

 higher animals. In the amoeba, a little animal 

 which is nothing more than a mass of jelly-like 

 living material, we find no trace of organs, and 

 nutrition is carried on by any part of the body. 

 But as we ascend in the scale of animal life, one 

 organ after another is added, such as a digestive 

 sac, glands for secretions to act on the food, a 

 special fluid the blood, an organ and 

 for circulating this fluid ; and so on, 



vessels 

 till we 



sweat, or as invisible vapour ; his kidneys act 

 similarly, the water in both cases containing salts 

 and other matters in solution ; and his lungs are 

 always exhaling, not only watery vapour, but the 

 gas known as carbonic acid, as maybe readily shewn 

 by breathing into lime-water, which soon assumes 

 a milky appearance, in consequence of the forma- 

 tion of carbonate of lime. Moreover, the body, 

 which has an almost constant temperature of 

 about 98-4 F. is always giving off heat. The 

 production of heat indicates chemical changes 

 in the body, accompanied by waste of material. 

 If this condition of things were to go on indefi- 

 nitely, the weight of the body would gradually 

 diminish. To retain the body in its normal state, 

 we must therefore supply it with three things 

 atmospheric air, -water, and food. We have placed 

 them in the order of their importance. 



Various classifications of the food of man have 

 been proposed ; but the following is simple and 

 practical : (i) the aqueous, (2) the albuminous, (3) 

 the/atf/y, oily, or oleaginous, (4) the saccharine, (5) 

 the gelatinous, and (6) the saline groups. All our 

 daily food is referable to one or more of these 

 classes. The aqueous group includes not only 

 water, but all fluids (except oils) used as drink, 

 and it must be recollected that all our so-called 

 solid foods contain a large percentage of water. 

 The albuminous group (often termed the protein) 

 is typified by the white of egg, and includes the 

 gluten of flour, the chief constituents of flesh 

 and cheese. These substances contain the four 

 elements, carbon, hydrogen, oxygen, and nitro- 

 gen, and also a little sulphur or phosphorus, or 

 both. The albuminous foods chiefly nourish the 

 muscles, but they contribute, along with fat or 

 oil, to almost every tissue. The fatty group in- 

 cludes all animal and vegetable fats or oils. They 

 are composed of carbon (ranging from 60 to 80 

 per cent.), hydrogen, and a little oxygen. The sac- 

 charine (often termed the starchy or amyloid) group 

 contains all the varieties of sugar, starch, dex- 

 trine, and gum ; like the preceding group, they are 

 composed solely of carbon, hydrogen, and oxygen. 

 Both the fats and sugars belong to the group 

 termed by chemists hydrocarbons, because they 

 contain carbon or charcoal, and oxygen and hydro- 

 gen, in the proportions, or nearly in the propor- 

 tions, necessary to form water. They contribute 

 chiefly to the adipose or fatty tissue of the body. 

 The gelatinous group is represented by cow-heel, 

 isinglass, and such-like substances, yielding jellies 

 and soups that stiffen on cooling ; while the salitu 

 group includes mineral matters, especially common 



come to the higher animals, where we find great i salt, and phosphates of the alkalies, and of lime, 



differences in parts, and corresponding differences 

 in function. We will divide nutrition into the 

 following thirteen stages, namely: 



I. FOOD, OR ALIMENT. 



A living being is always in a state of change. 



His skin gives off water, either in the form of \ of sapidity or. flavour in 

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&c. The" saline or mineral matters form bone, 

 tooth, &c. and they are found in variable propor- 

 tions in almost every fluid and solid in the body. 

 It must be remembered, however, that a mixture 

 of all of these constituents of food is essential to 

 the formation of a nutritious diet, and, moreover, 

 that there must always be a certain amoun 

 the food. 



\Ye should 

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