Journal of Applied Microscopy. 



55 



THE WEISS COLONOMETER. 



ONE-HALF ACTUAL SIZE. 



3=19.6350 square 

 4=38.4846 square 

 5=63.6174 square 

 6=95.0334 square 

 7=132.7326 square 

 circle 8=176.7150 



plate. The ratios are whole numbers as 

 follows: Ratios between areas of circles 

 2:1=9; 3:1=25; 4:1=49; 5:1=81; 6:1=121; 

 7:1=169; 8:1=225. Areas of the circles are 

 as follows: Area of center circle and 

 any sector circle =.7854 square centi- 

 meters, area of circle 2=7.0686 square 

 centimeters, of circle 

 centimeters, of circle 

 centimeters, of circle 

 centimeters, of circle 

 centimeters, of circle 

 centimeters, and of 

 square centimeters. 



Formula: (A Hypothetical Case.) 

 Area of plate equals that of circle 6. 

 The average number of colonies in a sec- 

 tor circle=12. But ratio of circles 6 to 1 

 is 121; therefore the entire number of 

 colonies on plate=12Xl21=1452. 



The calculating is evidently very sim- 

 ple and the colonometer is therefore of 

 very practical value to the bacteriolo- 

 gist. 



From the Bacteriological Laboratory 

 of the New York State Veterinary Col- 

 lege, Cornell University, Ithaca, N. T. 



A Holder for Collodion Imbed- 

 ding. 



Tissues imbedded in collodion have to 

 be secured by collodion to a block or 

 holder, which is then fastened in the 

 jaws of the microtome. To prevent 

 deposits occurring, if cork be used, and 



to secure a block that will not be com- 

 pressed by the microtome holder 

 (thereby often distorting the object), 

 wood has been recommended. The fol- 

 lowing wood holder has given excellent 

 results and was used by the writer and 

 his students in the botanical laboratory 

 of the Ohio State University. 



The holders are cut from basswood 

 (Tilia americana) of a size adapted to 

 the object holder of the microtome. I 

 found very convenient blocks fifteen mil- 

 limeters square and thirty millimeters 

 long. In one end of these a hole is bored 

 about five milimeters in diameter and 

 not over fifteen millimeters long. 

 Enough mercury is now poured into this 

 hole to sink the holder in alcohol and 

 the hole is then plugged tightly with a 

 piece of the same wood. Another advan- 

 tage of this holder is that both ends can 

 be employed, which is a convenience 

 when both longitudinal and cross sec- 

 tions are desired. A permanent number 

 can be placed on each holder for the 

 convenience of students in keeping track 

 of their material in the hardening jar. 

 No precipitates of any consequence will 

 arise from either the wood or mercury. 

 These blocks are best placed in weak 

 alcohol to keep them free from air, and 

 are then ready for use at any time. 



E. Mead Wilcox. 



Laboratory of Veg. Physiology, Har- 

 vard University, Cambridge, Mass., Feb. 

 8, 1898. 



