NUTKITION AND AVASTE. 13 



Serous Uuid, which we find in recent serous cysts (p. 333), and which is 

 secreted by serous membranes, closely resembles plasma. In health it does 

 not appear to contain any white corpuscles, and consequently, then shows no 

 tendency to coagulate. Under the influence of inflammation, or even of con- 

 gestion, there is a greater or less numerous migration of white corpuscles, 

 with the result that their presence in serous fluid gives rise to the deposition 

 of fibrin. It thus difl'ers from serum, which, being deficient of fibrin-forming 

 material, camiot coagulate. Excessive action of serous membranes [e.g. as a 

 result of inflammation) in the head, chest, and testicles, for instance, produces 

 respectively, water on the brain, hydrothorax (p. 354) and hydrocele (p. 291). 



NUIRITION AND WASTE.— Assuming for the present that immediately 

 before a contraction of the heart, the blood which is in the left ventricle is in 

 a state of comparative purity, it passes with but little alteration through the 

 arteries of general circulation, the walls of which are comparatively im- 

 pervious to fluids. Having arrived in the capillaries, the pressure on the 

 blood-stream forces a portion of the plasma thiough the thin walls of the 

 capillaries, so that plasma constantly bathes all the tissues, which take up 

 from it the materials required by them for nourishment and repair. Here, 

 the walls of the capillaries appear to act as a filter to the plasma, in keeping 

 back a large j)roportion of the fibrin constituents, so that transuded plasma 

 has no tendency, in health, to coagulate in the tissues. In the capillaries, 

 the red corpuscles part with more or less of their burden of oxygen to the 

 tissues. Under normal conditions, the red corpuscles remain in the blood- 

 vessels ; but a few of the leucocytes pass, from time to time, through the 

 walls of the capillaries into the tissues, probably to furnish fibrin-ferment to 

 the transuded plasma, or to remove waste matters. In health, excess of 

 plasma and waste products given off by the tissues, are drained away by a 

 system of vessels, called lymiihatics, which pour their contents into the veins. 

 The absorbent action of the lymphatics is supplemented, to some extent, by 

 that of the capillaries and veins. When the blood arrives in the right 

 ventricle, it is accordingly in an impure condition and has consequently 

 changed the bright scarlet colour which it wore when quitting the left 

 ventricle, to that of a bluish purple. This impure blood, after being pumped 

 from the right ventricle, gives off into the air-cells of the lungs the carbonic 

 acid which it received from the tissues, and taking up a fresh supjDly of oxygen 

 from the air in the aii'- cells, arrives bright-coloured and more or less pure in 

 the left auricle, from which it flows into the left ventricle, ready for another 

 circuit. Besides the lungs, other organs, such as the kidneys, skin and liver, 

 remove impurities from the system. 



DISTRIBUTION OF BLOOD IN THE BODY.— Under normal circum- 

 stances, the amount of blood in the body is just sufficient for its requirements. 

 Hence, if the blood supply be increased or decreased in one part, it will, 

 respectively, be decreased or increased in the remamder of the system. Thus, 

 mental work, or muscular exercise, if indulged in soon after a full meal, will 

 be liable to more or less interfere with the process of digestion, by " drawing " 

 the blood away from the internal organs, to the brain or muscles, as the case 

 may be. The feeling of drowsiness (due to a state of comparative bloodless- 

 ness of the brain) experienced after eating, is caused, to a great extent, by the 

 blood-vessels which supply the organs of digestion, being unusually full at the 

 time. The feeling of sleep or even faint'ness when taking a hot bath and the 

 relief of " fulness of blood in the head" by placing the feet in hot water, 

 illustrate the same fact. Here we have an explanation of the benefit — in cases 

 of inflammation of the organs of breathing, for instance — of warm fomentations 

 to the surface of the body and of counter-irritation (p. 17). 



AN^jSHA or bloodlessness may be either local or general. In the former 

 case, it may, as we have just seen, be OAving to congestion in other parts ; 

 and can also be brought about by cold, pressure, and diminution of the 



