BY DR. KLEIN. 145 



different parts. It is, however, better to cut one of the halves 

 transversely into a number of parts, which may be placed in a 

 large bottle filled with half or one per cent, solution of bichro- 

 mate of potash. After from eight to ten days, sections of the 

 cortex are prepared, as thin as possible. Some of these must 

 he made in the direction of the pyramidal processes (which are 

 readily seen by the naked eye), others at right angles to these 

 processes, and parallel to the surface. Other sections com- 

 prising as much of the medullary substance as possible, must 

 in like manner be made in both directions. The cross sections 

 should be taken from various parts of the medullary substance, 

 some comprising the papillae, others the intermediate part. 

 The sections, having been washed in water for fifteen minutes 

 or more, may be either mounted at once in glycerin, or after 

 previous staining for twenty-four hours in diluted solution of 

 carmine. Such preparations show the characters of the epi- 

 thelium in the tubes throughout their whole extent, and in the 

 loops of Henle. It may be further seen that in many of the 

 convuluted tubes of the cortex, the uniformly granular sub- 

 stance can be distinguished into distinct polyhedral cells, eacli 

 possessing a spheroidal nucleus. By teasing the sections ob- 

 tained as above, it is possible to isolate straight tubes or loops, 

 but this can be better accomplished by another method to be 

 described further on. 



Epithelium of the Malpighian Capsules. For the 

 demonstration of the epithelium which lines the internal 

 surface of each Malpighian capsule, and the surface of the 

 glomerulus, it is best to employ kidneys of mature or imma- 

 ture human foetuses. With this view the organ (which must 

 be as fresh as possible) must be divided into small portions, 

 and first placed for three to six days in one per cent, solu- 

 tion of bichromate of potash, and then transferred for one or 

 two days into one-fourth to one-eighth per cent, solution of 

 chromic acid. The sections are prepared in the ordinary way 

 after embedding. In such preparations it is seen that the 

 capsule of the glomerulus, which is characterized by its oblong 

 nuclei, extends continuously over it, and that it is lined with 

 a continuous layer of elements which are mostly cubical, but 

 sometimes columnar. The epithelium of the convoluted tubes 

 consists, in the human foetus, of spheroidal or cubical cells. 

 If a very small strip of the fresh kidney of the frog is pre- 

 pared in salt solution or serum, it is seen that the epithelium, 

 as well of the capsule as of the commencement of the con- 

 voluted tube leading from it, is beset with cilia of extraordi- 

 nary length. 



Isolation of the Tubes. Long slices of fresh kidney so 

 cut as to include both cortical and medullary substance, and 

 to extend from the surface to the papilla, are placed in a flask 

 10 



