HUMAN PHYSIOLOGY. 



sugar, and the latter, in dissolving flesh and other 

 albuminous bodies. 



The line of demarcation between the small and 

 large intestine is very obvious, and by the peculiar 

 arrangement of the ileo-caecal valve, which guards 

 the entrance of the small into the great intestine, 

 matters are allowed to pass forward with facility, 

 while regurgitation is impossible. The contents 

 of the large intestine differ very materially from 

 those which are found in the small intestine, and 

 constitute the faeces. They are more solid and 

 homogeneous, and are often moulded into a defi- 

 nite shape. The only essential change which the 

 contents undergo in this part of their course is, 

 that they increase as they pass onward in solidity, 

 in consequence of the absorption of fluid from 

 them by the mucous membrane. They are pro- 

 pelled onwards into the rectum by the vermicular 

 action which has been already described, and are 

 at last expelled by a voluntary effort. 



The fasces consist partly of undigested materials 

 and partly of matters which are derived from the 

 mucous membrane of the great intestine. It is in 

 the great intestine the chyme first acquires a faecal 

 odour, which increases in intensity as the material 

 passes along the bowel. This odour is not due 

 simply to putrefaction, but to the presence of 

 peculiar effete matters, which are thrown off by 

 the lining membrane of the bowel 



7. ABSORPTION OF NUTRITIOUS MATTER. 



As the chyme is propelled along the alimentary 

 canal, the watery portion, holding various sub- 

 stances in solution, is absorbed by the blood- 

 vessels, while the fatty matter is taken up by the 

 lacteals. It is believed that this absorptive action 

 is really a physical process dependent on osmotic 

 action. The whole of the nutritive material thus 

 separates itself into two parts : one which passes 

 directly into the blood, and the other which enters 

 the lacteals, and in these becomes a milky fluid 

 called the chyle. It is important to remember that 

 all the blood circulating in the digestive organs 

 must pass through the liver before entering the 

 general circulation, and from it the cells of the 

 liver select and elaborate their secretions. But 

 the chyle passes into the blood indirectly. It is 

 first conveyed to numerous glands in the neigh- 

 bourhood of the intestines, called mesenteric 

 glands. Before entering these glands it is a milky 

 fluid, essentially molecular ; but after it has passed 

 through the glands it is found to contain small, 

 round, biconcave discs, termed chyle corpuscles, 

 along with much molecular matter. The lacteal 

 vessels proceeding from these glands unite with cor- 

 responding sets of vessels from the lower limbs, 

 called lymphatics, in a wide cavity opposite the last 

 dorsal vertebra, the receptaculum chyli. From 

 this cavity a duct, the thoracic duct, ascends 

 through the thorax, receives branches from 

 the left arm and left side of the head, and 

 unites with the venous system at the root of the 

 neck on the left side, the point of junction being 

 where the left internal jugular vein unites with 

 the great vein of the left arm, the left subclavian. 

 The lymphatics of the rest of the body unite to 

 form the right lymphatic duct, which joins the 

 venous system at a corresponding point on the 

 opposite side. The whole of the chyle, therefore, 

 passes into the blood at the root of the neck ; from 

 thence it goes through the right side of the heart 



to the lungs, where the corpuscles probably 

 acquire colour, and become the coloured corpus- 

 cles of the blood. 



8. SANGUIFICATION. 



By this term we mean the making of blood. In 

 the lowest animals, such as in the amoeba, we 

 find no circulating nutritious fluid When we 

 ascend higher in the scale we find a colourless fluid 

 containing molecules moving in certain definite 

 directions by the action of cilia in the general 

 cavity of the body, as in a sea-anemone. Still 

 higher we meet with a colourless fluid circulating 

 in vessels, frequently communicating with the 

 body-cavity, and propelled by a special contractile 

 organ, as in the sea-urchin or ascidian ; and at 

 last we meet with a coloured fluid, circulating in 

 vessels separate from the body-cavity, and having 

 a propelling organ, or heart, of more or less 

 complex structure, as in all the vertebrata. This 

 fluid, in the higher animals and in man, is derived 

 from three sources : ist, from materials absorbed 

 in the primary digestion of the food in the ali- 

 mentary canal ; 2d, from the secretions of certain 

 glands called blood-glands, found in various parts 

 of the body ; and, 3d, from materials re-intro- 

 duced into the blood from the tissues, which are 

 products of the decomposition and solution of 

 portions of these tissues consequent on their vital 

 activity. The so-called blood-glands are the 

 spleen, a large organ found almost in juxtaposition 

 with the left end of the stomach ; the suprarenal 

 capsules, two organs found in the lumbar region, 

 one on the top of each kidney; the thymus, a 

 gland found in the thorax, immediately behind the 

 breast-bone, of larger size before birth and during 

 the earlier years of life than during adult life ; the 

 thyroid, a gland existing in front of the box of 

 the larynx ; the pituitary and pineal glands, 

 found in the brain ; the glands of Peyer, in the 

 mucous membrane of the small intestine ; and 

 lastly, the lymphatic glands, which we find in 

 many parts of the body, such as in the groin, 

 the armpit, the neck, &c. and which we 

 readily recognise as hard 'kernels' during the 

 inflammation of any adjoining part. All of these 

 glands agree in certain points of their anatomy ; 

 they have no ducts to carry off the secretion, 

 except we regard the numerous lymphatics by 

 which they are supplied as such ; they consist 

 essentially of shut sacs, containing numerous 

 molecules, nuclei from which cells may be de- 

 veloped, and fully formed cells resembling white 

 blood corpuscles ; and finally, they are richly 

 supplied with blood-vessels, lymphatics, and 

 nerves. That they are really connected with the 

 formation of blood, more especially of the colour- 

 less corpuscles, is probable from the fact, that in a 

 disease known as leucocythaemia, in which there 

 is a great increase in these cells, we find also that 

 one or more or all of the blood-glands are much 

 enlarged. 



9. THE BLOOD AND ITS CIRCULATION. 



The blood is the most important and most 

 abundant fluid in the body, and deserves the 

 popular term of the ' vital fluid.' With the excep- 

 tion of a few tissues, such as the centre of 

 the cornea of the eye, the nails, and the hair, 

 it pervades every part of the body, as may t 



