HISTOLOGICAL DEMONSTRATIONS. 121 



hours, and then the mixture is" replaced by distilled water, in which 

 they are left for a day. The tubules are then isolated by shaking a 

 slice in a test tube, with a little water. 



f. The epithelium lining the Malpighian capsules is best demon- 

 strated in the kidney of the child at birth. Cut it into small pieces. 

 Place them in I per cent potassium bichromate solution for a week, 

 then in ^ per cent chromic acid for a day, and make sections in the 

 freezing microtome. 



g. The blood-vessels may be readily injected with gelatine and 

 carmine, etc., as described in 342. 



208. Structure. Examine V. S. Malpighian pyramid 

 without the aid of the microscope ; the whitish compact 

 medullary substance near the apex of the pyramid ; the 

 softer reddish-brown cortex at the base. The longitudinal 

 striae in the medullary substance are due to the straight 

 tubules. The pyramids of Ferrein bundles of the straight 

 tubules are easily seen where the medullary passes into 

 the cortical substance. The red lines between these pyra- 

 mids are due to the vasa recta. In the cortex it is just pos- 

 sible to see fine granulations on the cut surface, produced 

 by the glomeruli. Tear off the fibrous capsule, and in so 

 doing notice the fine filaments that appear to be torn 

 across ; these are capillaries that pass between the cortex 

 and the capsule. 



209. V. S. Malpighian pyramid of cat's kidney hardened 

 in Mailer's fluid, as described in 9, cut in the freezing 

 microtome, and stained with logwood. Mount in Farrants' 

 solution or in glycerine. 



(L.) Trace the tubules from the apex of the Malpi- 

 ghian pyramid into the cortex. The tubules are straight in 

 the medulla, and form bundles the pyramids of Ferrein 

 towards its outer part These pass nearly to the outer part 

 of the cortex. In the cortex the straight tubules give off 

 lateral branches that become the convoluted tubules, and 

 finally end in the capsules enclosing the glomeruli. These 

 lie amidst the convoluted tubules, and can be readily re- 

 cognised. 



(H.) The glomerulus or Malpighian body a cluster 

 of capillaries enclosed in a capsule formed by expansion of 

 the basement membrane of a convoluted tubule lined by 



