and Laboratory Methods. 2463 



the front is formed of a thick cover-glass cemented on the ring ; '10 is a cell made 

 by cementing a thick cover-glass — square rather than a circle — over three-fourths 

 of the hollow in an ordinary hollow-ground slide like 3 ; 21 is a closed ring cell 

 made by cementing a glass ring on a plate glass slide ; and 22 is a better form 

 of ring cell, because of the larger surface for attachment to the slide. 



The most generally useful forms are numbers 1, 3, 6, 7 or S, 10, 11, 13, 14, 

 15, 17, 18, and 22. Number 14 is improved by cementing it on a glass plate as 

 in 17, and it may be used with many organisms for which 11, 13, and 17 are 

 preferable. 



For fish three or four inches long, crayfish, large tadpoles, and objects of 

 similar size a large glass cell made like 16 with a length of about seven inches, 

 height and thickness from front to back as great as the kntern will carry, is most 

 desirable. Some dealers in projection apparatus sell these under the name of 

 " alum tanks," those made entirely of glass well cemented being preferable to 

 the kinds made of glass plates with metal and rubber fittings. 

 University of Chicago. A. H. COLE. 



A simple apparatus for the anserobic cultivation of bacteria, based upon the 

 well known property of an alkaline solution of pyrogallic acid to absorb oxygen, 

 consists of a battery-jar in which the cultures are placed on a suitable support. 

 Ov^er them is placed an inverted tin can or a sheet of tin foil, and over this 

 some absorbent gauze and an inverted battery-jar. Water is poured into the 

 outer jar so as to form a water-seal. A mixture of pyrogallic acid and caustic 

 potash is introduced through a bent tube passing under the edge of the inner 

 inverted jar and opening within the apparatus above the gauze, so that the latter 

 is kept moistened by fresh absorbent solution falling upon it drop by drop. The 

 outer end of the tube is connected with rubber tubing to a separatory funnel 

 placed at a higher level than the jars. The solutions of pyrogallic acid (20 per 

 cent.) and caustic potash (30 per cent.) are mixed in this funnel under a layer 

 of paraffin oil, to prevent oxidation of the mixture. At first the gauze is stained 

 dark brown ; when absorption is complete, a white spot appears where the ab- 

 sorbent solution falls upon the gauze. The rubber connection, with the 

 separatory funnel, can then be broken, and the absorbent solution in the bent 

 tube acts as a water-seal. The oxygen is removed from the jar in about thirty 

 minutes, and an anaerobic condition can be maintained for at least five days. 

 The whiteness of the gauze is the guarantee that oxygen is excluded. — Exchange. 



