228 EXPEHIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



anotlier is secured by means of the nervous system, v/hicli 

 regulates at once tlie activity of any organ, the quantity of 

 nutritive fluid supplied to it, and the amount of material it shall 

 take up. The means by which it acts are, its direct influence 

 on the nutrition of cells themselves,* as is seen in the salivary 

 glands ;t or its indirect action through the circulation in slowing 

 or quickening the heart, which propels the blood ; in contracting, 

 or dilating the vessels which convey it to any part ;i or, on the 

 capillaries which allow the actual nutritive fluid or lymph to 

 filter out and bathe the tissues. l]esides thus regulating the 

 supply, it also regulates the composition of the nutritive fluid 

 by maintaining a due relation between the activity of the body, 

 the supply of new material by digestion, and the separation of 

 effete products by the excreting glands. On account of this 

 mutual dependence of all the parts of the body on one another, 

 if one gets wrong it puts the others out of order. Thus a 

 sudden chill may act on the vaso-motor nerves, and cause con- 

 traction of the vessels of the skin ; the blood they contain is 

 thus thrown back on the internal vessels § and congestion and 

 inflammation of the kidneys ensue. In consequence of this, 

 they no longer excrete as they ouglit tlie effete products, which 

 then accumulate in the blood, react on the nervous system, and 

 this again on the muscles ; and so the circle goes on. In the 

 case supposed, the vaso-motor nerves of the kidneys have also 

 been retlexly affected by the chill, and in consequence the renal 

 arteries have not contracted sufficiently to resist the increased 

 pressure and prevent congestion ; while in another tliey might 

 have done so, only allowing so much blood to j)9'''S as to in- 

 crease secretion, a^d, by thus lessening the flow in the renal 

 vessels have counteracted the effect of ^'ascular contraction in the 

 skin, restored the normal pressure in the kidneys and preserved 

 health. When all the organs are able to accommodate their 

 nutrition and function to great alterations, we say the health 

 is strong ; but when they can only do so to slight ones, we say 



* Ludwig, Physiologic d. Menschen, vol. ii, p. 316. 



f Heidenhain, Studien aus d. Fhysiolog. Institut zu Breslau, Heft iy, 1SG8. 



X Ean^ier, Compt. rend., 18G9, vol. ii, p. 1320. 



§ Tide JoliBson, British Medical Journal, Dec. Gtli, 1873, p. 064. 



