WITH THE MICROSCOPE. 9 1 



4. Tissues prepared by this process can be subjected to examina- 

 tion, by powers magnifying more than 5,000 diameters. See part V. 



5. All tissues may be mounted in aqueous preservative solutions, 

 and the most delicate structures are retained in their integrity. 



6. By this process of injection alone can the alteration of the 

 most delicate tissues, which occurs very soon after death, be pre- 

 vented. 



It will be seen that several important principles are involved in 

 this new process, which will be more fully enunciated in part V. 



Of late years carmine fluid has been much used for transparent 

 injections, especially in Germany ; but although many of these speci- 

 mens are very beautiful, I am not aware that new facts have been 

 revealed by the process. As the specimens are mounted in balsam, 

 the structure of the tissues external to the vessels is completely lost. 

 Moreover, the vessels with the contained injection have become 

 much reduced in diameter by the process of drying, and generally the 

 appearances seen cannot be regarded as natural. 



All that is to be learnt by such modes of preparation, has been 

 already learnt. For more minute investigation it is absolutely neces- 

 sary that the tissue be prevented from undergoing post-mortem 

 change, and that it be preserved in some viscid aqueous fluid. By drying 

 the tissue its structure is often destroyed. The only mode of prepa- 

 ration by which injected textures can be subjected to examination 

 by the highest powers, and which permits of all the several structures 

 entering into their composition being displayed in the same specimen, 

 is that which I am advocating in conjunction with the staining process 

 described in part V. 



In order to inject the vessels for examination by transmitted light 

 several different substances may, however, be used as injecting fluids ; 

 but if it is desired to study the tissues as well as the arrangement of 

 the vessels, the points just adverted to must be borne in mind. 



175. Injection with Plain Size. A tissue which has been 

 injected with plain size, when cold is of a good consistence for 

 obtaining thin sections, and many important points may be learnt 

 from a specimen prepared in this manner which would not be 

 detected by other modes of preparation. A mixture of equal parts 

 of gelatine and glycerine is, however, much to be preferred for this 

 purpose, and the specimen thus prepared is sure to keep well. Very 

 thin sections of spongy tissues like the lung maybe most successfully 

 made after injection with strong gelatine or gelatine and glycerine. 



176. Colouring Matters for Transparent Injections. The chief 

 colouring matters used for making transparent injections are carmine 

 and Prussian blue. The former may be prepared by adding a little 



