. Physiology, experimental and descriptive . ld be double-urinarycone , the space between the inner and outer layerscontinuous with the hollowof the handle. Instead ofa solid ball held by onestring, there should be ayarn ball with two largestrings attached to oneside, one representing theartery, the other thevein; the yarn ballnal represents the dense cluster o f capilla-ries. A still betterillustration of the urinarytube and capsule may bemade thus : Take a thistle tube (used in the chemical labora-tory), let down into the bulb a rubber balloon or bag of sheet-rubber or cloth, fastenin
. Physiology, experimental and descriptive . ld be double-urinarycone , the space between the inner and outer layerscontinuous with the hollowof the handle. Instead ofa solid ball held by onestring, there should be ayarn ball with two largestrings attached to oneside, one representing theartery, the other thevein; the yarn ballnal represents the dense cluster o f capilla-ries. A still betterillustration of the urinarytube and capsule may bemade thus : Take a thistle tube (used in the chemical labora-tory), let down into the bulb a rubber balloon or bag of sheet-rubber or cloth, fastening the margin around the rim of thebulb; put a little ball of red yarn in the depression of thebag hanging in the bulb; have two ends of the yarn project-ing to represent the artery entering and the vein leaving thecapsule. The vein, soon after it emerges, breaks up intoanother set of capillaries which extend around the tube. Anumber of these primary tubes unite, and many of the com-mon ducts open at the apex of each of the urinary pyramids,. UreterFig. S3. Cross Section of Kidney. SKIN AND KIDNEYS. 165 emptying their secretion into the cavity of the kidney. Asthe. blood flows through the tuft of capillaries in the Capsuleat the end of the tube, a good deal of water, together with saltand some other substances, passes through the thin partitioninto the cavity of the capsule, and thence down the tube. Thewalls of the tube are thicker than, and its cells are differentfrom, those of the capsule. These ceHs take the urea andsome other substances from the blood, and pass them into thetube to join the more watery material from the capsule. Comparison of the Skin and the Kidneys. — The kid-neys, then, are not very different from the skin. Imagine apiece of skin rolled up with its outer surface turned inward. Its glandsNthen would pour their se-cretions into a cavity wherethey might accumulate in-stead of evaporating asfast as they are pouredout. Of course thekidneys have
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