WITH THE MICROSCOPE. 2 1/ 



and in the majority of instances the coagulation is associated with a 

 certain opacity quite incompatible with the satisfactory examination 

 of the tissue by transmitted light, and as I have before hinted, it is 

 absolutely necessary to render such a specimen transparent after the 

 thin section has been obtained, p. 144. It is well to bear in mind that 

 before we can submit many soft structures to microscopical exami- 

 nation,, we have to consider what chemical substances- are likely to 

 harden them in the most advantageous manner for cutting thin sec- 

 tions, and if by this process the section be made opaque we have 

 further to consider how its natural transparency may be restored. The 

 chemical nature of the substance to be examined, its physical proper- 

 ties, its refractive power, and its chemical composition, are points 

 which it is most desirable that every microscopic observer should be 

 acquainted with before he commences any particular investigation. 



I have succeeded in rendering the tissues of the embryos of mam- 

 malian animals so transparent that the smallest ossific points can be 

 seen in the temporary cartilages. To dissect these bony points at so 

 early a period, would be a work of immense labour, but by merely 

 soaking the whole organism in the solution, they become beau- 

 tifully distinct. The embryo is to be immersed in alcohol to- which 

 a few drops of solution of soda have been added, and allowed 

 to remain in it for a few days. When the action has taken place, it 

 is to be removed and preserved permanently in weak spirit. I have 

 a beautiful preparation of this kind which has been kept for upwards 

 of ten years. The principle of the action of the fluid may be 

 explained thus : alcohol alone tends to coagulate albuminous tex- 

 tures and render them opaque, at the same time tiivat it hardens 

 them. The alkali, on the other hand, will render the tissues soft 

 and transparent, and, if time were allowed, would cause their com- 

 plete solution. These two fluids in conjunction harden the texture 

 and at the same time make it clear and transparent. Many soft tissues 

 may thus be hardened sufficiently to enable us to cut very thin sections. 

 Preparations of this kind show how much may be effected by the 

 use of very ordinary chemical reagents. By this simple process, a 

 minute dissection which would occupy many days is avoided, the 

 chance of losing some of the small ossific points is prevented, while 

 the structures are displayed far more distinctly than they could be 

 by the most careful dissection. 



Doubtless there are many other fluids yet to be applied to the 

 purposes of investigation of much greater value than the present one, 

 and I strongly recommend observers to take up this branch of the 

 enquiry and endeavour to discover new modes of preparing textures 

 which shall render their minute structure clearly demonstrable. 



