i8g 3 . SOME USEFUL METHODS IN MICROSCOPY. 123 



When a difficult object has to be cut, a small quantity of the 

 mixed mastix-celloidin solution is put into a tube or small bottle, and 

 diluted with ether mixed with a little absolute alcohol until it is quite 

 thin and fluid. We will suppose that, meanwhile, the block of 

 paraffin containing the embedded object is fixed in position on a 

 Jung microtome, or some similar kind of instrument, ready to be cut. 

 Before cutting each section the surface of the paraffin block is painted 

 over with the thin mastix-celloidin solution by means of an ordinary 

 soft paint brush. It almost instantaneously sinks in a little way into 

 the paraffin, and, in the same instant, the ether evaporates, leaving the 

 mastix-celloidin mixture behind. The excess of the mastix-celloidin 

 is then rubbed off with the finger, and the surface of the paraffin block 

 should be polished with the finger by rubbing it several times. If now 

 a section is cut, it will be found to be held together by the mastix- 

 celloidin mixture which has penetrated into the object, and thus pre- 

 vents the breaking up of the section that so often follows when yolk or 

 chitin is cut. By this simple, if rather tedious, method, I have 

 obtained uninjured series of sections not only through eggs containing 

 yolk, but also through the thorax of a large mygaloid spider, in which 

 the chitin had not been softened in any way. I have sometimes also 

 found it necessary for things stuck on liver, as the liver is liable to 

 become very brittle. 



E. A. Minchin. 



