ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 247 



are incubated at 37 • 5° C. If organisms be present, a clouding of the 

 bouillon and blackish discoloration of the blood at the bottom of the 

 flask gives evidence of their growth within 24 to 48 hours. Occasionally 

 the signs of growth do not appear for four or five days. The bacilli are 

 afterwards identified on the ordinary media and by the agglutination 

 test. Cultures made early in the disease give a much higher percentage 

 of positive results than those made during the third or fourth week. 



Method of Concentrating Plankton without Net or Filter.* — . 

 B. L. Seawell describes the following procedure for concentrating 

 plankton. The samples are collected by dipping or by the use of a 

 plankton pump without the filter. A measured quantity, say 500 c.cin., 

 is placed in a conical flask of, say 750 c.cm. capacity, 5 c.cm. of 40 p.c. 

 formaldehyde added, and the two well mixed at once. The planktonts 

 soon die and settle at the bottom. After about a week the supernatant 

 fluid is siphoned off till only 150 c.cm. remain. The residue is poured 

 into a conical flask of about 150 c.cm. capacity, and allowed to settle 

 for another week. The siphoning is repeated and the residue poured 

 into a 75 c.cm. flask. This flask has a base so small in diameter that 

 all but about 20 c.cm. can be safely siphoned off, and this last sediment 

 filled into two 10 c.cm. phials. If kept for future study it may be 

 advisable to add a small quantity of glycerin. 



(2) Preparing Objects. 



Bleaching Reagents.f — S. E. Dowdy remarks that hydrogen per- 

 oxide when used as a bleaching agent should be employed fresh and of 

 full strength. Chlorinated lime in freshly prepared solution, to which 

 a drop or two of dilute acid is added, makes a much more satisfactory 

 bleacher. 



Formol-sublimate Fixing Fluids.:}:— R. Pearl recommends the fluids 

 devised by D. C. Worcester for fixing and killing. One of these is a 

 saturated solution of sublimate in 10 p.c. formalin. The other consists 

 of nine parts of the foregoing and one part of glacial acetic acid. 

 The first fluid is especially adapted for fixing and killing Protozoa ; the 

 second for fixing teleost eggs, and embryological material in general. 



(3) Cutting:, including- Imbedding- and Microtomes. 



Pleuel Microtome. § — In this instrument which has been improved 

 by Kaplan, the movement is given to the knife-carrier through the 

 continuous turning of a handle, to the crank of which a connecting- 

 rod is attached in the desired degree of eccentricity. This rod is at its 

 other end connected with a sliding block, to which it gives a to-and-fro 

 movement. The sliding block is joined to a metal band, which in its 

 turn is loosely connected to the knife-carrier by means of a double- 

 hinge joint. The extent of the to-and-fro movement of the knife- 



* Trans. Amer. Micr. Soc, xxiv. (1903) pp. 17-19. 

 + English Mechanic, lxxix. (1904) p. 63). 

 % Journ. Applied Micr., vi. (1903) pp. 2451. 

 § P. Thate's Catalogue, Berlin, 1903. 



