OUTLINE FOR LABORATORY STUDY OF THE CHICK 33 1 



the tissue begin slightly to adhere. Then slowly add the killing 

 fluid by aid of a pipette, dropping it on the center of the embryo. 

 The pipette miist be held low or the mechanical interference will 

 dislocate the parts. 



Older embryos are submerged with their membranes intact into 

 the killing fluid. The quantity of fluid should be several times the 

 bulk of the specimen. Kleinenberg's picrosulphuric acid may be 

 used as a killing fluid. This fluid is a saturated solution of picric 

 acid plus 2 per cent, sulphuric acid, to which is added twice its 

 volume of water. 



Chick embryos from one to two days old should be left in this 

 fluid from one and one-half to six hours. Embryos from two to 

 four days old two and one-half to sLx.hours. Remove the specimen 

 from the killing fluid, and place it in 70 per cent, alcohol. Change 

 the alcohol every twenty-four hours until the color ceases to come 

 out of the embryo. Preserve in 80 per cent, alcohol. 



If the specimen is to be mounted whole, transfer it from 80 per 

 cent., then to 50 per cent., then to 35 per cent., and, finally to 

 water. Small embryos should remain in each fluid thirty minutes 

 and large ones sixty minutes. 



The following method may be used for staining embryos: Dilute 

 Delafield's hematoxylin with four times its volume of water. To 

 every 6 cubic centimeters of this diluted hematoxylin, add one drop 

 of Kleinenberg's undiluted picrosulphuric acid, and leave specimen in 

 the fluid thus prepared until it is stained through. This will require 

 from one to three hours. Now pass up through the series of alcohols 

 to 70 per cent. Next extract the excessive stain with i per cent, 

 hydrochloric acid in 70 per cent, alcohol. Wash repeatedly with 

 70 per cent, alcohol to free from the acid; then transfer the specimen 

 to 80 per cent, alcohol and leave in this for several hours for com- 

 plete removal of the acid; then transfer to 95 per cent, alcohol for 

 thirty minutes. Allow the specimen to remain in absolute alcohol 

 for one hour. Introduce a layer of oil of cloves or xylol beneath the 

 alcohol. This may be done by gradually allowing the fluid to run 

 down the side of the bottle. After the embryos have sunk into the 

 oU and begun to appear transparent, remove the fluid and add fresh 

 oil. After the specimen is suflSciently transparent, mount in 

 balsam, supporting the cover slip so that it will not rest on the 

 embryo. 

 ' In staining for section, place the embryo in borax carmine from 



