194 PRACTICAL HISTOLOGY [XXV 



the pyramids of Malpighi, run to the outer portion of 

 the intermediate layer, and there form a network more 

 complete in the case of the veins than in that of the 

 arteries. 



2. Section 1 of mammalian kidney transverse to its 

 long axis extending from the outer surface to the 

 summit, or nearly to the summit, of a papilla (ammonium 

 bichromate 5 p.c.). Stain with picrocarmine. 



a. Observe under a low power 



The medulla, with its straight collecting tubes; 

 some of the numerous divisions of these as they run 

 outwards may be seen, but they are not conspicuous 

 (cp. Demons. 1). 



The intermediate layer : the collecting tubes of 

 the Malpighian pyramids separate into bundles the 

 medullary rays; between the bundles are seen 

 numerous small blood vessels and some tubes of 

 Henle (cp. 2, b). At its outer limit are one or 

 more large blood vessels. 



The cortex: the medullary rays are seen to run 

 out nearly to the free surface, between these are 

 convoluted tubes and glomeruli, the latter arranged 

 as a rule in two rows between each two rays (the 

 symmetrical arrangement of the medullary rays and 

 intervening convoluted tubes will not be obvious if 

 the section is cut obliquely). In the extreme outer 

 part of the cortex convoluted tubes only are seen. 



1 In cutting out the piece of kidney for sections, the cortical part 

 should not be thicker than the pyramid near its- summit, otherwise 

 the medullary portion in some of the sections will be cut too obliquely. 



