208 HARDENING OF INJECTED MATERIAL. 



material must be cut into small cubes, and its power of rendering 

 micro-organisms z/«stainable. For objects in bulk, as amputations, 

 small or large animals, if an opening be made in the abdomen 

 and thorax, so the fluid will penetrate, Miiller is the best agent, 

 and it does not interfere with the staining of micro organisms. 

 Its objections are the length of time it takes, and the slight 

 colouring of the tissues by the potassium bichromate, though 

 this, by frequent washing with running water, can be aided, pre- 

 vious to the tissue being put into weak spirit to the strong, or by 

 a 5 per cent, solution of hydrate of chloral. Chromo-osmic 

 acetic acid is also good for small tissues. 



The main point to be remembered is, we require to fix the 

 elejtients as soon after death as possible, by an agent which will not 

 contract the tissues too suddenly, by abstracting the water too quickly 

 a?td coagulatifig the albumen. These methods of hardening are 

 the best also for injected tissues, if used ice cold when the gelatin 

 masses are employed. I find a good way is to use the solution of 

 Miiller to keep the animal in whilst injecting with hot masses, as 

 gelatin, instead of the ordinary hot water. 



Mbi? Xeavee Cbange Colour* 



A BOTANIST has thus explained in Forest and Stream why 

 leaves change colour : — The green matter in the tissues of 

 a leaf is composed of two colours — red and blue. When 

 the sap ceases to flow in the fall and the natural growth of the tree 

 ceases, oxidation of the tissue takes place. Under certain condi- 

 tions, the green of the leaf changes to red ; under different 

 conditions, it takes on a yellow or brown tint. This difference in 

 colour is due to the difference in combination of the original con- 

 stituents of the green tissue and to the varying conditions of 

 climate, exposure, and soil. A dry, cold climate produces more 

 brilliant foliage than one that is damp and warm. This is the 

 reason that the American autumns are so much more gorgeous 

 than those of England. 



There are several things about leaves that even science cannot 

 explain. For instance, why one of two trees growing side by side, 

 of the same age and having the same exposure, should take on a 

 brilliant red in the fall and the other should turn yellow ; or why 

 one branch of a tree should be highly coloured and the rest of the 

 tree have only a yellow tint, are questions which are as impossible 

 to answer as why one member of a family should be perfectly 

 healthy and another sickly. 



