KIDNEYS. 85 



nucleated plates, and therefore not unlike blood-vessels. The ascending limb (7) in its 

 wide part is lined with polyhedral ' rodded ' cells, with their nuclei next the innermost part of 

 the cells. The narrow ascending part (8) is lined with low polyhedral cells, and has a very 

 narrow lumen. The collecting tubes are lined with a single layer of homogeneous transparent 

 nucleated cells, which vary considerably in shape. 



It is to be remembered that the above arrangement has only been made out after laborious 

 investigations, and no such complete tubule was ever seen, or can ever be seen, in a section of 

 a kidney. The course of the tubules can only be made out by isolating the tubules as 

 described at p. 86. 



PREPARATION, a. Chromic Acid and Spirit Mixture. Remove the kidneys from an animal 

 just killed by bleeding rabbit, dog, or cat ; divide one transversely into several pieces with a 

 sharp razor, and place them in the above fluid. Take great care, in order not to separate the 

 capsule. Divide the other longitudinally and treat it in the same way. Make both transverse 

 and longitudinal sections of the kidney. Stain some with logwood and mount either in 

 dammar or in Farrant's solution, whilst others maybe stained with picrocarmine and mounted 

 in Farrant's solution. 



b. Muller's fluid may be employed in the same way as the above, but takes from three to 

 four weeks to complete the hardening. 



c. Ammonium Chromate (Heidenhain). Harden small pieces in a five per cent, solution of 

 ammonium chromate for forty-eight hours, then wash away all the colouring matter, and 

 complete the hardening in dilute, and then in strong spirit. 



Prepare portions of a normal linuian kidney in the same way (a and c). Compare sections 

 of these with the above. 



KIDNEY OF A RABBIT OR DOG. 



Transverse Section. EXAMINATION. With the naked eye note the general shape of the 

 section, distinguishing the capsule, which is very easily detached from the cortex. Note the 

 division of the parcnchy ma into three distinct regions : the cortex, the boundary layer (Ludwig) 

 and the papillary portion, the two last forming the medulla, which terminates in a papilla, 

 projecting into the pelvis of the kidney. 



(L). In the medulla observe the radiating rows of straight tubules (tiibuli recti) proceeding 

 from the pelvis outwards. As they pass outwards they divide dichotomously. When taken 

 collectively they constitute a Malpighian pyramid. In the cortex observe that on the boundary 

 line between it and the medulla, the straight tubules of the Malpighian pyramid are continued 

 as bundles of straight tubules into the cortex, constituting the pyramids of Ferrein, or me- 

 dullary rays, which are the direct continuation of the straight tubes of the medulla into the 

 cortex. As they radiate towards the capsule these bundles of tubules become smaller, and 

 are always separated from the capsule by a layer of convoluted tubules. Observe the convo- 

 luted tubules (tiibuli contorti] confined to the cortex. They lie between the pyramids of 

 Ferrein, and between their upper ends and the capsule. Between two pyramids of Ferrein 

 observe the double row of Malpighian corpuscles, which consist of the capsule of Bowman in- 

 closing a glomeruhis, or tuft of blood-vessels. Sometimes the glomeruli fall out, and then 

 there is only a circular aperture in the section. Notice under the capsule more or less tri- 

 angular spaces, which are transverse sections of veins. Observe how easily the capsule sepa- 

 rates, and note the very limited amount of connective tissue which passes from its under 

 surface into the organ. {Indicate the shape of the kidney and the general arrangement of the 

 tubules in PI. XIX., Fig. I.) 



