and Laboratory Methods. 



2587 



GENERAL LABORATORY TECHNIQUE. 



RAYMOND PEARL, University of Michigan. 



Books and Papers for Review should be Sent to Raymond Pearl, Zoological Laboratory, 

 University of Michigan, Ann Arbor, Mich. 



A Mechanical Rocker for Developing In American Medicine for August :i2, 

 Negatives. 1 i*08, p. 303, Dr. G. E. Pf ahler describes 



a very neat device which he has 

 invented for rocking the developing pan during the development of photographic 

 negatives. The apparatus was devised especially for use in Rontgen-ray work, 

 but will be found equally useful in all sorts of laboratory photographic work. 

 The apparatus consists of the motor of an electric fan, from which the fan has 

 been detached. This is done by loosening a single screw, and in place of the 

 fan is attached a pulley 1 inch in diameter. The belt then runs over a wheel 



Fig. 1. 



12 inches in diameter to which a pulley 1 inch in diameter is attached. This 

 turns a wheel 12 inches in diameter having an arm attached 1^2 inch from the 

 center, which gives the rocking base a sway of 3 inches. The pulley on the 

 motor revolves 1000 to 3000 times per minute. This rocks the pan from 10 to 

 20 times per minute, according to the regulation of the amount of the current. 

 The pulley on the motor can be replaced by the fan in less than half a minute, 

 which can then be used to fan the plates dry. Details of the apparatus are 

 shown on the illustration, Fig. 1. R. p. 



Schultze's Method of Preparing Vertebrate 

 Embryos to Show Ossification. 



Preparations of embryos made by 

 Schultze's method, in which the ossified 

 portions of bones appear as white 

 opaque objects, while all other tissues are transparent, are among the most strik- 

 ing and useful of embryological preparations. The method of making them 

 seems not to be generally known, and as the only place where it is published (so 

 far as known to the reviewer) is in Schultze's " Grundriss der Entw^icklungsge- 

 schichte des Menschen und der Saugethiere " (Leipzig, 1896). it seems desirable 



