XXVIII.] KIDNEY. 3O7 



sublimate is also very good, and so is alcohol. The pieces should 

 not be large, and should be cut according as a longitudinal or trans- 

 verse section is desired. Stain and cut in bulk in paraffin. In all 

 cases the pieces should include both the cortical and medullary 

 portions, and should not be more than half-an-inch in thickness. 



(ii.) Place small pieces in boiling water and then complete the 

 hardening in Miiller's fluid or alcohol. 



(iii.) To fix the epithelium use Flemming's fluid, e.g., for mouse's 

 kidney. 



Make radial sections from the cortex to the apex of a Malpighian 

 pyramid. For a general view stain a section in haematoxylin and 

 mount it in balsam. Another one should be stained in picro- 

 carmine or picro-lithio-carmine and mounted in Farrant's solution. 

 For unstained sections, steeping them for twenty-four hours in 

 i per cent, osmic acid before mounting them in Farrant's solution 

 is excellent. The best way is to begin with a section of the entire 

 kidney of a small animal, such as- a mouse, rat, or guinea-pig. In 

 this way a good view is got of the entire organ in section. 



1. Radial Section of Kidney of a small mammal. 



(a.) (L) Observe the capsule ; it is thin and apt to fall off; the 

 cortical and medullary portions of the parenchyma. The medulla, 

 composed of straight tubules of different sizes, and running radially 

 from the pelvis of the kidney outwards. 



(b.) Trace some of the straight tubules outwards through the 

 intermediate layer, in bundles the pyramids of Ferrein or medul- 

 lary rays into the cortical layer (fig. 293, PF). Many medullary 

 rays pass from a Malpighian pyramid, and they run radially out- 

 wards in the cortex nearly to its outer part although they do not 

 reach the surface becoming narrower as they are traced outwards. 



(c.) In the cortex, between every two medullary rays, are con- 

 voluted tubes, twisted and cut in every direction, and two rows of 

 glorneruli, enclosed in their capsules the labyrinth. Here and 

 there a glomerulus may have fallen out, and the space it occupied 

 be left as a round aperture. The regular arrangement of the 

 glorneruli will only be seen provided the section runs parallel to the 

 course of the medullary rays. The glomeruli are confined to the 

 cortex, but none of them reach quite to the capsule. 



(<l.) (H) In the cortex, the Malpighian capsules, each enclosing 

 a tuft* of capillaries or glomerulus. They consist of a structureless 

 membrane lined by a single layer of squames. The oval, flattened 

 nuclei of the latter are seen lying on the inner surface of the cap- 

 sule. Within each capsule a cluster of capillaries glomerulus 

 arranged, in several groups. Although the squamous lining of the 

 capsule is reflected over the capillaries, it is not easy to distinguish 

 the nuclei of these cells from the very numerous nuclei of the 



