354 THE AMERICAN MONTHLY [Nov., 



off nearly all the essential oil left in it, by long continued mod- 

 erate heat ; the residual resin is then made slightly less brittle, 

 by dropping into it, when melted, an exceedingly small por- 

 tion of castor oil ; it is easy to add too much of the latter. The 

 object is to get a transparent cement which will neither crack 

 with age nor permit the formation of aborescent markings be- 

 tween the glasses from evaporation of essential oil. — Photo- 

 American. 



To Prevent Vegetable Sections Turning Dark. — Soak in 

 alcohol to which 2 per cent of hydrochloric acid has been added 

 and let them dry slowly. 



Bleaching Leaves. — Chlorinated soda is the best fluid for 

 bleaching vegetable specimens. 



BIOLOGICAL NOTES. 



Blood Measurements. — In The Microscope for May. 1886, 

 was published a paper by Dr. A. Waterhouse giving the results 

 of years of labor in measuring blood corpuscles. He had hoped 

 to be able to distinguish human blood from that of lower ani- 

 mals. As we have frequent calls for that number, which is out 

 of print, we repeat here the gist of all that the article contained. 

 His method, after many experiments with different methods 

 was to use fresh blood spread upon a thin glass cover so thinly 

 that the corpuscles should not touch each other and become 

 disturbed. He warmed it gently so that the blood should dry 

 quickly, A ring was made with cement on a slide and the 

 cover inverted upon it so that the blood would be on the under 

 side of the cover. The ring keeps the blood from touching the 

 slide and forms a closed cell. In it the blood keeps for years. 



The measurements were made with a fine 1-16 inch objective 

 and D eye-piece micrometer giving a magnification of about 2,- 

 800 diameters. Value of his eye-piece micrometer was deter- 

 mined by a stage micrometer ruled by Prof W. A. Rogers, to 

 1-2500 of an inch. The relative length of tube, from eye-piece 

 to objective, was kept the same, and the collar adjustment was 

 placed at the same point of correction. 



His largest corpuscles were those of the foetus of grey gopher 

 (1-2,009 in.) and the smallest those of the goat (1-7,031 in.). 



