164 THE ESSENTIALS OF HISTOLOGY 



LESSON XXXIII. 



STRUCTURE OF THE KIDNEY. 



1. SECTIONS passing through the whole kidney of a small mammal, such as a 

 mouse or rat. These sections will show the general arrangement of the organ 

 and the disposition of the tubules and of the Malpighian corpuscles. 



A general sketch should be made of one of these sections under a low 

 power. 



2. Thin sections of the kidney of a larger mammal, such as the dog, may 

 next be studied. In some the direction of the section should be parallel 

 with the tubules of the medulla, and in others across the direction of those 

 tubules. The characters of the epithelium of the several parts of the uriniferous 

 tubules are to be made out in these sections. 



3. Separate portions of the uriniferous tubules may be studied in teased 

 preparations from a kidney which has been subjected to some process 

 which renders it possible to unravel the uriniferous tubules for a certain 

 distance. 1 



4. Sections of a kidney in which the blood-vessels have been injected. 

 Examine these with a low power of the microscope. Try and follow the 

 course of the arteries those to the cortex sending their branches to the 

 glomeruli, those to the medulla rapidly dividing into pencils of fine vessels 

 which run between the straight uriniferous tubules of that part. Notice also 

 the efferent vessels from the glomeruli breaking up into the capillaries which 

 are distributed to the tubules of the cortical substance. 



Make sketches showing these points. 



The kidney is a compound tubular gland. To the naked eye it ap- 

 pears formed of two portions a cortical and a medullary the latter 

 being subdivided into a number of pyramidal portions (pyramids of 

 Malpighi), the base of each being surrounded by cortical substance, while 

 the apex projects in the form of a papilla into the dilated commence- 

 ment of the ureter (pelvis of the kidney). 2 Both cortex and medulla 

 are composed entirely of tubules the uriniferous tubules which have 

 a straight direction in the medulla and a contorted arrangement in the 

 cortex ; but groups of straight tubules also pass from the medulla 

 through the thickness of the cortex (medullary rays). 



The uriniferous tubules begin in the cortical part of the organ in 

 dilatations, each enclosing a tuft or glomerulus of convoluted capillary 



1 For a method which may be employed for this purpose, see Course of Prac- 

 tical Histology, p. 209. 



' 2 In many animals the whole kidney is formed of only a single pyramid, but 

 in man there are about twelve. 



