514 MANUAL OF HISTOLOGY. 



generally to be about the average amount secreted by the adult human 

 being daily ; though we must admit that this statement is based upon 

 very uncertain data. 



As to the use of bile in the processes of digestion, we know that it 

 possesses no fermenting power over the albuminates, but precipitates on 

 the contrary albuminous substances from their acid solutions whether 

 digested or undigested. It has the same effect on pepsin. It is still a 

 debated question, whether it possesses the power of transforming starch 

 into sugar. It saponifies the free fatty acids, and forms an emulsion with 

 fat, thus facilitating its absorption by the intestinal villi (Bidder and 

 Sch midt, Wistingli ausen) . 



Besides this, as Bidder and Schmidt have shown, the greater part of the 

 bile, in fact almost all its water, as well as |ths of its solid constituents, 

 is again taken up into the circulation by absorption from the intestines ; 

 but nothing farther is known as to what changes its constituents undergo 

 there. In a changed state the pigmentary matters pass through the intes- 

 tine, together with a small quantity of cholestearin, and occasionally some 

 taurin. The products of the metamorphosis of choleic acid are also met 

 with, namely, choloidinic acid and dyslisin. Neurin also and glycero- 

 phosphoric acid also partake of the nature of decomposition products. 



The development of the liver, although still a knotty point in his- 

 tology, has been cleared up to a great extent by the important dis- 

 coveries of Rernak. From these it would appear that the organ springs 

 very early from the cells of the so-called gland layer in the form of two 

 saccules, clothed externally by a fibrous envelope, derived from the walls 

 of the intestine, and which has been pushed before the growing saccules. 

 From the most internal cells of these primitive bile ducts, solid groups of 

 elements are produced by a process of division, the " hepatic cylinders," 

 which advance in their farther growth into the external enveloping layer, 

 dividing in their progress, arid branching with the formation of networks. 

 Those cells of the originally external envelope, which have become as it 

 were entangled within the meshes of the network formed by the hepatic 

 cylinders, are gradually converted into fibrous or connective tissue, vessels 

 and nerves, while the secreting elements of the gland are to be found in 

 the cells of the hepatic cylinders. It is a fact of great interest, first 

 pointed out by Bernard, that at an early period of intra-uterine existence 

 the liver contains no glycogen, although this is to be found in the placenta, 

 the epidermal cells, and epithelium of the intestine, as well as in the 

 passages of the glands developed from the latter, and also in muscle 

 ( 170). With the development of the liver the disappearance of glycogen 

 commences at one point early, at another later, continuing until birth. 



4. The Urinary Apparatus. 

 269. 



The urinary apparatus consists, as is well known, of two glands : the 

 kidneys (designed to secrete the urine), and a system of excretory pas- 

 sages made up of the ureters, which terminate in a common reservoir, the 

 bladder, and the urethra, by which the fluid is eventually carried off from 

 the latter. 



The kidney, Ren, a large bean-shaped organ with a smooth surface, is 

 covered by a thin but strong fibrous envelope, the tunica propria, which 

 is continued on to the external surface of the infundibula at the hilus, 



