133] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 13 



of the specimen chamber. This tube must be bent in the shape of an S to 

 raise the specimen chamber to a point where the outlet is above the lowest 

 part of the mixing chamber to keep the apparatus from running dry. The 

 same result can of course be obtained by inserting the specimen chamber 

 under the mixing chamber and bending up the outlet tube to a point above 

 the top of the specimen chamber. 



This apparatus was for this work preferred to the Cobb type because 

 it permitted the dehydration of a large amount of material at one time and 

 so saved an infinite amount of labor. 



When the specimens were dehydrated they were removed from the 

 chamber into a small stendor dish and cleared in xylene by means of the 

 string differentiator described by Magath. This consists essentially of 

 three dishes placed one above the other like steps in a stairway. The upper 

 dish contains the liquid to be introduced, the middle dish contains the 

 specimens, and the lower one the waste. The liquid is transferred from 

 dish to dish by means of string siphons. The string drawing the liquid 

 from the specimen dish does not reach the bottom of that dish and so 

 prevents the removal of all the liquid from the specimens when the upper 

 dish goes dry. The whole apparatus is covered by a bell jar sealed at the 

 bottom to prevent the alcohol from absorbing moisture from the air. 



This differentiator was later adapted also for dehydrations. The chief 

 objection to the use of the apparatus described by Magath for dehydration 

 lies in the fact that the stronger alcohol introduced into the specimen dish 

 tends to form a layer at the top and is drawn off again by the second string, 

 increasing only very slowly the strength of the lower alcohol, causing an 

 enormous waste of liquid, and usually ruining the specimens. It is possible 

 to withdraw the alcohol from the bottom of the specimen dish by means of 

 a capillary glass tube bent in the shape of a U. This capillary tube must 

 widen out rather suddenly at the outlet to an inside diameter of about two 

 millimeters and this end must be bent outward so that the liquid drops 

 freely from the tube without touching the dish. If this tube is not widened 

 at the outlet it is impossible to keep the alcohol in the specimen dish at 

 the proper level on account of the different effect of capillarity on the 

 different grades of alcohol. An ordinary capillary tube that will keep water 

 at the proper level will drain the dish completely when the higher grades 

 of alcohol are used. The level at which the liquid will be maintained is 

 determined by the position of the outlet of the capillary tube as the liquid 

 will stop flowing when the level tends to become lower and will start 

 automatically when that level is raised. For clearing specimens dehyd- 

 rated in this differentiator the capillary tube is replaced by a string. 

 This apparatus is by far the most convenient and the safest for delicate 

 specimens as they can be kept in the same dish thruout the entire process 

 of dehydration and infiltration. 



