41 8 SECRETION OF THE URINE. [sect. 190. 



latter kind, urea, afford the most obvious instances. Thus there 

 appears to arise in the commencements of the tubules a very 

 diluted urine, which then, during its passage towards the pelvis of 

 the kidney, enters into mutual relation with the blood bathing the 

 tubules, takes up from it new materials, (probably more urea), and 

 gives off, at the same time, certain of its constituents, such as 

 water and salts. Thus it becomes, for the first time, urine, in the 

 proper sense of the word. 



We know very little about the chemical composition of the 

 kidneys. Frerichs (I.e. p. 42) found in a healthy kidne}^ i6'3 to 18 

 per cent, of solid parts (Lang 181 to 20 per cent.), with 72 to 737 

 parts of water. Of the solid portion, the fat amounted to 063 to 

 i'o per cent., still, according to 0. Rees, it may increase to r86 

 (Lang finds 2*0 to 2'8 per cent, fat; in one case, the medulla con- 

 tained 1*7, the cortex, 2*4). The greater part, however, appears to 

 be albumen, Ludivig, more especially, having shown that it exists 

 in large quantities in the kidney ; and this cannot be surprising, 

 when we consider the micro-chemical condition of the epithelial 

 cells of the urinary tubules. 



An important addition has lately been made to our knowledge 

 of the chemistry of the kidneys, in the discovery by Cloetta of 

 inosite, hypoxanthin (or xanthin), cystin and taurin, in the sub- 

 stance of the organ. Bechmann has also established the existence 

 of leucin and tyrosin. The occurrence of these substances renders 

 it very probable, as Bechmann has pointed out, that certain con- 

 stituents of the urine are real products of the kidney, and are not 

 merely separated by this organ from the blood. 



The secretion of the urine takes place in the higher animals without the 

 formation and solution of cells ; and, accordingly, the normal newly secreted 

 urine contains no morphological elements, with the exception of a few 

 fat-drops (Lang). It is only accidentally that we find epithelial cells in 

 it, and these are derived from the excretory passages, especially the bladder 

 and urethra ; but mucus from the same localities is almost always present, 

 as a slight turbidity or sediment occasionally containing mucous corpuscles : 

 spermatozoa, too, may be found, after evacuation of semen. In inflammations, 

 hemorrhages, exudations, and formation of fat in the kidneys, the urine con- 

 tains pus corpuscles, fat-globules, blood-discs, or coagula of blood and fibrine. 

 These are aggregated into cylindrical plugs, which are casts of the urinary 

 tubules ; and besides these, we meet with epithelium of urinary tubules, 

 either isolated or arranged in connected strings or tubes. Sediments of the 

 salts of the urine are very readily formed in consequence of decomposition. 

 Normal urine without sediment, exposed for a while to a moderate tem- 

 perature, always passes into an acid fermentation by the action of the con- 

 tained mucus. Along with the fungi thus produced, the colouring matter 



