122 THE MICROSCOPE. 



injections of the human subject. But with the chemico- 

 gelatinous injections no such preparation is necessary; and 

 success should always be certain, for the potash liquefies 

 the blood, while constant and long-continued pressure by 

 the syringe drives it through the parietes of the vessel 

 into the cellular tissue." 



Transparent Injections. " Much more strongly," writes 

 Dr. Beale, "can I recommend to you the use of transparent 

 fluids for making injections. It is true, that these are not 

 likely to be so much admired by general observers as 

 opaque injections. Indeed, it is not easy to find any 

 object which will rival in beauty many tissues which have 

 been freely injected with vermilion or chromate of lead; 

 although it must be confessed that from such preparations 

 we learn but little save the general arrangement of the 

 capillary vessels of the part, their capacity, and the mag- 

 nitude of the meshes of the network. Of the relations 

 which these vessels bear to the elementary structures 

 which give to the texture under examination its peculiar 

 properties, such preparations tell us nothing. Opaque 

 injections are for the most part only adapted for examina- 

 tion with low powers, while the tissues to which the vessels 

 are distributed can only be seen with the help of very high 

 magnifying powers. Transparent injections, on the other 

 hand, though they fail to excite the wonder of the un- 

 initiated, show us not only the general arrangement of 

 the capillary network, but the precise relation which 

 each little tube bears to the tissue with which it is in 

 contact. 



" In order to make injected preparations for examination 

 by transmitted light, several different substances may be 

 used as injecting fluids. 



" Injection with Plain Size. A tissue which has been in- 

 jected with plain size, when cold is of a good consistence 

 for obtaining thin sections, and many important points 

 may be learned from a specimen prepared in this manner 

 which would not be detected by other modes of prepara- 

 tion. 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. 



" Colouring Matters for Transparent Injections. The chief 



