30 PRACTICAL HISTOLOGY. 



nuclei of the endothelial plates. Observe the small lymph-corpuscles in the meshwork. Not 

 unfrequcntly in the mesenteric glands of the ox certain of the lymph-cells will be found to 

 contain a brownish-coloured pigment, and I have found multi-nucleated cells closely resembling 

 those found in the spleen. The source of the pigment in the one case, and the origin and function 

 of these multi-nucleated cells, have still to be investigated. In the silver preparation certain 

 parts acted on by the silver are brown, while those unacted on are bluish from the logwood 

 stain. The silver opens up the network somewhat, and thickens the fibrils of which it is 

 composed, so that it is more easily seen. It forms an instructive preparation. (Indicate the 

 characters of adenoid tissue in PI. V., Fig. 7.) 



BONE. 



PREPARATION. Methods of softening bone, (a) Chromic and nitric acid. Dissect out a 

 long bone the femur or humerus of a cat or rabbit remove the muscles attached to it, but 

 retain the periosteum. With a saw cut the bone into pieces three-quarters of an inch in 

 length, and place them in a bottle with 300 cubic centimetres of one-sixth per cent, solution 

 of chromic acid (p. xxxi). After three days substitute a quarter per cent, solution of chromic 

 acid, and after three days more a half per cent, for another three days. Then transfer the 

 pieces of bone to a large quantity of a mixture of chromic and nitric acid (p. xxxiii). The 

 object is to remove the calcareous matter and leave the structure of the bone intact. The 

 chromic acid alone ' fixes ' the elements and partially decalcifies the bone, but to employ 

 chromic acid solution alone requires a long time to complete the decalcification, hence the use 

 of chromic and nitric acid mixture, which completes the process more rapidly, with no risk of 

 the more delicate structures in the bone being injured by the action of the nitric acid. It 

 expedites the process to change the fluid frequently. At the end of three weeks the bones 

 still retain their form, though flexible and soft, and can now be cut with a knife. By thrusting 

 a needle into the bone one can determine when all the calcareous matter has been removed, there 

 being an absence of grittiness. The bone will now have a greenish colour, from the deposition 

 of a chromic sesquioxide. Place the bone in a large quantity of water, frequently changed to 

 get rid of the acids. Either make sections (transverse and longitudinal) at once in the usual 

 way, or place the bones in alcohol till they are required. 



() Picric acid method. Place similar pieces of bone in a saturated solution of picric acid 

 and add a few crystals of the acid to keep the solution saturated, as part of the acid is used up 

 to combine with the lime in the bone. This process takes much longer time than the above, 

 but it answers admirably for fcetal bones or for very small bones. After decalcification wash 

 the bones for a long time in water, to get rid of the intensely yellow colouring matter. Place 

 them in spirit till they are required. Make transverse sections of the shaft of a bone, including 

 the periosteum, decalcified in either of the above ways. Place some of the sections in a 

 one per cent, solution of osmic acid for twelve hours. Wash them thoroughly and preserve 

 them in weak spirit. 



(c) A 10 per cent, solution of sodic chloride and hydrochloric acid. This is for showing the 

 fibrillar structure of the bone-matrix (v. Ebner and De B. Birch). This method is fully de- 

 scribed at p. xxxiii. The sections must be preserved in a ten per cent, solution of sodic chloride. 



(d) Artificial digestion with trypsin. See p. xxxiv. 



