THE URINARY ORGANS. 595 



take place varies very much. Simon places the commencement of the 

 atrophy between the eighth to the twelfth years, a statement which, 

 from my own observations, and in accordance with those of Ecker, I 

 cannot consider as universally correct ; because, up to the twentieth 

 year, the tliymus is frequently met with in a good state of nutrition, 

 distended with fluid, without any fatty metamorphosis, and presenting 

 the same structure as in children. It is still more difficult to assign the 

 time of its complete disappearance, for which no determinate age can 

 be indicated, although it is true that the thymus is usually not to be 

 found after the fortieth year. The disappearance takes place in con- 

 sequence of a gradual absorption, with a simultaneous development of 

 fat in the gland-granules, and of fat-cells in the interlobular connective 

 tissue. At the same time, also, the concentric corpuscles multiply 

 more and more, and ultimately, according to Ecker, even connective 

 tissue is developed in the lobules, the glandular structure being com- 

 pletely lost. 



% 



The investigation of the tliymus is not easy. I recommend, in the 

 first place, boiled preparations, which of themselves are very well 

 adapted for the investigation of the connection of the lobes with the 

 central canal, and the cavities in the lobules, and when hardened in 

 spirit are convenient for the making of fine sections. Besides this, the 

 hardening of recent preparations in alcohol, pyroligneous and chromic 

 acid, and the boiling of them in acetic acid, are advisable. The thy- 

 mus, also, of small Mammalia, which is membranous at the edges, is 

 well adapted to afford a general knowledge. But, moreover, and above 

 all, are injections of the human thymus indispensably requisite, without 

 which no satisfactory conclusions can be arrived at. 



Literature. S. C. Lucae, " Anat. Untersuchung. d. Thymus im 

 Menschen und in Thieren," Frankfurt am M. 1811 u. 12, 4to, und 

 "Anat. Bemerk. uber die Divertikel am Darm. u. die Hohlen des 

 Thymus," Numb. 1813, 4to ; F. C. Haugsted, " Thymi in horn, et per 

 ser. animal descrip.," Hafn., 1832, 8vo ; A. Cooper, "Anatomy of the 

 Thymus Gland," Lond., 1832, 4to ; J. Simon, " A Physiological Essay 

 on the Thymus Gland," Lond., 1845, 4to ; Ecker, Art. " Blutgefass- 

 driisen," in Wagner's " Handw. der Phys." III. 



OF THE URINARY ORGANS. 



185. The urinary organs consist of the two kidneys true glands, 

 having a tubular structure, which secrete the urine and of the secre- 

 tory urinary passages, the ureters, bladder, and urethra. 



186. In the kidneys, are to be distinguished the coatfsand the secre- 



