44 MATERIAL COMPOSITION OF MAN. 



thorax or chest contains the lungs organs of respiration and the 

 heart, the central organ of the circulation. The abdomen contains the 

 principal organs of digestion, and (if we include in it the pelvis), those 

 of the urinary secretion and of generation. Of the limbs, the upper, 

 suspended on each side of the thorax, are instruments of prehension; 

 and are terminated by the hand, the great organ of touch. The lower 

 are beneath the trunk ; and are agents for supporting the body, and 

 for locomotion. Vessels, emanating from the heart, are distributed to 

 every part, conveying to them the blood necessary for their life and 

 nutrition: these are the arteries. Other vessels communicate with 

 them, and convey the blood back to the heart the veins; whilst a third 

 set arise in the tissues, and convey into the circulation, by a particular 

 channel, a fluid called lymph whence they derive the name lymphatics. 

 Nerves, communicating with the great central masses of the nervous 

 system, are distributed to every part ; and lastly, a membrane or layer, 

 possessed of acute sensibility the skin serves as an outer envelope 

 to the whole body. 



It was before observed, that two kinds of elements enter into the 

 composition of the body the chemical or inorganic; and the organic, 

 which are compound, and formed only under the force of life. 



The chief CHEMICAL or INORGANIC ELEMENTS, met with, are oxygen, 

 hydrogen, carbon, nitrogen, phosphorus, calcium ; and, in smaller quan- 

 tity, sulphur, iron, manganese, calcium, silicium, aluminium, chlorine; 

 also, sodium, magnesium, &c. &c. 



1. Oxygen. This is widely distributed in the solids and fluids ; and 

 a constant supply of it from the atmosphere is indispensable to animal 

 life. It is almost always found combined with other bodies ; often in 

 the form of carbonic acid, that is, united with carbon. In a separate 

 state it is met with in the air-bag of fishes, in which it is found varying 

 in quantity, according to the species, and the depth at which the fish 

 has been caught. 



2. Hydrogen. This gas occurs universally in the animal kingdom. 

 It is a constituent of all the fluids, and of many of the solids; and is 

 generally in a state of combination with carbon. In the human intes- 

 tines it has been found pure, as well as combined with carbon and sul- 

 phur. 



3. Carbon. This substance is met with under various forms, in both 

 fluids and solids. It is most frequently found under that of carbonic 

 acid. Carbonic acid has been detected in an uncombined state in urine 

 by Front ; and in the blood by Vogel. 1 It exists in the intestines of 

 animals ; but is chiefly met with in animal bodies, in combination with 

 the alkalies or earths ; and is emitted by all animals in the act of re- 

 spiration. 



4. Nitrogen. This gas is likewise widely distributed as a component 

 of animal substances, and especially of the tissues. It occurs in an 

 uncombined state, in the swimming-bladder of certain fishes. 



5. Phosphorus is an essential constituent of neurine ; and is found 

 united with oxygen, in the state of phosphoric acid, in many of the 



1 Annals of Philosophy, vii. 56. 



