WITH THE MICROSCOPE. IO5 



tissues, such as the mucous membrane of the intestines or other parts, 

 have been injected, it is necessary to lay them perfectly flat, and wash 

 the mucus and epithelium from the free surface, either by forcing a cur- 

 rent of water from the wash-bottle, or by placing them in water and 

 brushing the surface gently with a camel's hairbrush. Pieces of a con- 

 venient size may then be removed and mounted in solution of naphtha 

 and creosote, in dilute alcohol, in glycerine, or in gelatine and glyce- 

 rine. The most important points in ordinary injections may be shown 

 if the preparation be dried and mounted in Canada balsam. The 

 specimen must, in the first place, be well washed and floated upon a 

 glass slide with a considerable quantity of water, which must be 

 allowed to flow off the slide very gradually. It may then be allowed 

 to dry under a glass shade, in order that it may be protected from 

 dust. The drying should be effected at the ordinary temperature of 

 the air, but it is much expedited if a shallow basin filled with sulphuric 

 acid be placed with it under the same bell-jar, p. 76, pi. XX, fig. 131. 



Of solid organs, such as the liver and kidney, thin sections from 

 the interior made in different directions, as well as portions from the 

 surface should be preserved. Thin sections may be made with the 

 ordinary scalpel or with Valentin's knife, if an extensive one be 

 required. The surfaces of the section should be well washed, and it 

 may then be mounted in one of the methods previously described. 



Specimens which have been injected with Prussian blue or car- 

 mine injecting fluids, the composition of which is given in pp. 93, 95, 

 must be preserved in glycerine containing a trace of free acetic acid 

 (5 to 15 drops to the ounce). The advantage of this plan is that it 

 enables us not only to observe the arrangement of the vessels, but 

 also to study all the other structures entering into the composition of 

 the tissue or orsan. 



6 



Injections as Moist Specimens and Mounted in Canada Balsam. 



The observer will be surprised at the great differences observed 

 in the same texture according to the method in which it is pre- 

 pared. I have already adverted to the objections of mounting moist 

 tissues in balsam. Although most observers in Germany still pursue 

 this plan for preserving their injections, it will be condemned as 

 unsatisfactory by any one who has tried the method of mounting 

 the specimen moist in strong glycerine. Not only are the nuclei of 

 the vessels for the most part destroyed by the process of mounting 

 in balsam, but many very important elements of the tissue, and espe- 

 cially nerve fibres, are so changed that they cannot be recognised, 

 or are completely obliterated. The capillaries themselves are so 

 shrunk and changed that very wrong conclusions would be arrived 



