90 THE AMERICAN MONTHLY [Mar., 



ject about 1-10 inch; these make the mark. By this time the 

 slide or slides — the writer always does a packet at a time — will 

 have become dry. Now work the gauge round the four sides of 

 the slide ; the result will be a small square absolutely central ; 

 also a maltese cross, the arms of which serve admirably as a 

 guide for placing the cover. Pack the slides close together in a 

 box alwavs with the marked face in one direction. Before using 

 a slide just quietly wipe off the chalk from the blank surface. 



To Cut Hard Chitinous Objects. — Minchin, while at the 

 Naples Laboratory, succeeded in cutting sections of eggs con- 

 taining yolk, such as cep^ialopods and other hard objects as 

 follows : 



Make two solutions in ether (1) of celloidin or collodium (2) 

 of gum mastix, having added a small quantity of absolute 

 alcohol. The celloidin should be as thick as possible and the 

 mastix as thick as syrup. Mix equal quantities of the two sol- 

 utions. 



When a hard object is to be cut, thin some of the mixture 

 with ether mixed with a little absolute alcohol until the mix- 

 ture is quite fluid. The object to be cut being embedded in 

 paraffin and placed in the well of the microtome, paint the sur- 

 face of the paraffin block with the thin mastix-celloidin solu- 

 tion by using a soft paint brush. The solution sinks into the 

 paraffin, the ether evaporates leaving the mixtures near the 

 surface of the block. Wipe off the excess and polish the sur- 

 face by rubbing with the finger. Now cut a section and behold 

 the matter held together in a strip iustead of crumpled and 

 scattered in fragments. Repeat the process of coating with 

 mastix-celloidin for each section cut and whole series of unin- 

 jured sections can be cut through eggs containing yolk, through 

 the thorax of an insect and many other refractory specimens. 



To Mount Protozoa. — A drop of water containing the 

 animals is placed in a slide and covered by a cover-glass sup- 

 ported at its four corners by wax feet. The drop should be free 

 from debris of all kinds. The wax feet should be high enough 

 to keep the organisms from being squeezed, but low enough to 

 keep them from rapid motion — the slip should just not touch 

 them. A drop of Hermann's or of Fleming's solution should 

 then be placed at the side of thecoverslip and cautiously drawn 

 through by blotting paper or filter paper being placed at the 



