4 6 PRACTICAL HISTOLOGY. 



P ACINI'S CORPUSCLES. 



PREPARATION. These are numerous in the mesentery and in the mesorectum of the cat, 

 where they are easily obtained free from fat. The student may also find them in the deeper 

 layers of a vertical section of the skin of the hand or foot, or in the pad of a cat's foot, but I 

 have found them most easily for students in transverse sections of an entire foetal leg or 

 arm. Being placed relatively closer to each other in the foetus, they are, like sweat-glands, 

 more easily observed there than in adult textures. 



In the cat's mesentery they can be seen as small, oval, transparent, hard bodies. Snip out 

 one of these and examine it at once in salt solution with a low power ; the nerve entering it 

 may be seen, as also the central core surrounded by concentric laminae. If a permanent pre- 

 paration be desired, excise a piece of the mesorectum or mesentery containing these bodies, 

 pin it out in a stretched condition on a flat piece of cork, and place the cork, tissue down- 

 wards, for a week, in a two per cent, solution of potassic bichromate ; after that wash away all 

 trace of the reagent with water, snip out a corpuscle and stain it slowly (twenty-four to forty-eight 

 hours) in dilute logwood, which must be changed several times. Wash in water and mount in 

 glycerine. As the corpuscles are of considerable thickness, it may be necessary to place a thin 

 layer of paper under the edges of the cover-glass to avert pressure, and allow the cover-glass 

 to lie flat upon the preparation. 



EXAMINATION (L). Observe the nerve-fibre like a stalk approaching and entering the 

 central core of the oval corpuscle, which latter is made up of laminae one outside the other. 

 (H). Trace the nerve-fibre, and observe that the medullary sheath stops where the nerve 

 enters the corpuscle. Only the axial cylinder passes into the central core. Study the con- 

 centric laminae, which exhibit a series of nuclei on each surface. These are the nuclei of the 

 endothelial cells which cover each lamina. 



To study the laminae and their endothelial covering, a corpuscle, hardened as above, must 

 be broken up with needles, by which process the various lamina; are readily separated from 

 each other. 



Transverse sections will be obtained in one or other of the preparations already mentioned. 

 These show the concentric distribution of the laminae round the central core, and also the 

 nuclei of the cells between each two laminae (p. 92). 



