530 MANUAL OF HISTOLOGY. 



tinal germinal plate, with an external fibrous layer, consequently in the 

 same manner as the lungs ( 243). Subsequently the uriniferous tubes 

 are developed from this system of cavities, in the form of solid bands 

 of cells, which become hollow at a later stage of development, acquiring 

 at the same time a membrana propria. The results of Kupffers obser- 

 vations, however, would seem to point to different conclusions. According 

 to him the organs in question are first developed in the form of saccules, 

 on the passages of the primordial kidneys or Wolffian bodies. 



274. 



From the investigations of Frerichs, it would appear that the kidney 

 (whose sp. gr. is placed by Krause and Fischer at 1*044 for the medulla 

 and 1*049 for the cortex) contains from 82 to 83 '70 per cent, of water. 

 Of the 18-16*30 per cent, of solid constituents, albumen seems to be the 

 largest in amount. The proportion of fatty matter is from 0*1 to 0*63 

 per cent. The tissue of the organ is alkaline here also during life, and 

 acid after death (Kuhne). As to the composition of the gland elements, 

 we know that the membrana propria partakes of the nature of the elastic 

 substances, while the contents and whole substance of the cells must be 

 looked upon as albuminous. The fatty molecules observed in the cell 

 bodies explain the amount of adipose matter found in the organ, which 

 varies considerably. 



The decomposition products of the kidney found in its juices are of 

 some interest. Among them appear inosite, hypoxanthin, xanthiri, and 

 at times leucin in considerable abundance (Staedtler). Further, in the 

 dog kreatin is to be found (M. Hermann}, in the ox, cystin and taurin 

 (Clo'etta). Most of these matters probably pass off in the urine. 



The urine is designed to carry off from the body the greater part of all 

 the water received into it, as well as the principal products of the decom- 

 position of histogenic substances, and also the excess of albuminous 

 matters received into the system as food. Finally, it eliminates all 

 mineral constituents set free in the interchange of material in the animal 

 economy, together with any excess of salts which may be present in the 

 alimentary matters. Taking all this into consideration, and especially 

 that its composition is materially influenced by the nature of the alimentary 

 matters, as far as quantity, wateriness, and chemical constituents are con- 

 cerned, we can easily conceive that it must be subject to considerable 

 variation even in normal states of the system, a variation which may 

 become even more strongly marked under pathological conditions, or the 

 influence of drugs which are partly eliminated through the kidneys. 



Healthy urine, freshly secreted, is a light yellow fluid of acid reaction, 

 bitter taste, and peculiar odour. Its sp. gr. varies greatly, according to 

 the proportion of water contained in it, and may range from 1*005 to 

 1*030, but usually lies between 1*015 and 1*020. The amount of urine 

 secreted in the course of the day varies also. It usually exceeds some- 

 what 1000' grammes, and may rise and fall between 1200 and 1800. 



On cooling a light cloud is generally found in animal urine, consisting 

 of mucus secreted by the urinary passages, especially the bladder, together 

 with the characteristic flattened epithelium of these parts, and a few 

 mucous corpuscles. 



The acid reaction which human urine exhibits when just voided, de- 

 pends not upon the presence of one or more free acids, for such are not tc 

 be found in it, but upon acid salts, and especially on phosphate of sodium. 



