344 THE AMERICAN MONTHLY [Nov 



sure to kill all bacteria that have penetrated the enamel 

 or dentine. 



When once the people fully realize that bacteria alone 

 are the cause of their soft, chalky teeth, and that it ia 

 possible to so harden the teeth that they will resist the 

 solvent action of bacteria, then the gilded and glaring 

 signs "painless extraction" will have to come down. Dent- 

 istry will become a profession loved by mankind, and to 

 be called a dentist an honor. — Pacific Medical Journal. 



Miscellaneous Notes on Microscopy. 



JOHN. a. COOKE, F. L. S., F. G. S. 



Cleaning Diatoms. — The addition of a little ammonia to 

 the water in which diatomaceous materials are being wash- 

 ed facilitates the removal of slimy, gelatinous products, 

 cleanses the diatoms, and hastens their settlement to the 

 bottom of the vessel. 



Pulverizing Rock. — To extract siliceous organisms from 

 rock fragments, heat the rock to about one hundred de- 

 grees Fahrenheit, and then plunge it into a boiling solution 

 of soda sulphate. This salt takes up water as it crystal- 

 lizes, and the rock, therefore, readily pulverizes under its 

 influence. 



Diatom Mounts. — Balsam of tolu, from which the cinna- 

 mic and benzoic acids have been removed by prolonged 

 boiling in a large quantity of water, is an admirable mount- 

 ant for diatoms. It should be dissolved in rectified ben- 

 zine, filtered, dried, and finally dissolved in alcohol or chlo- 

 roform. The refractive index of the balsam thus pre- 

 pared is 1.72 when dry. 



Double Stain.— Methyl-green is an effective double stain 

 for all vegetable sections. When applied to fibres, whether 

 of pure cellulose or of lignin, it produces a deep green if 

 the fibre has been mordanted before staining ; while a light 

 green is produced when the order of stain and mordant is 

 reserved. Apply in strong aqueous solution. 



Amoeba. — For the preparation of permanent mounts of 



