EXAMPLE 3 



Preparation of a Wholemount of 33-hour Chick 

 Embryo, Using the Alum Hematoxylin Stain 



of Delafield 



Fertile eggs are relatively easy to obtain and should be incubated at a 

 temperature of 103° F for the required period of time. The term "33-hr 

 chick" is relatively meaningless since the exact stage and development 

 that will have been reached after any given time in the incubator depends 

 on the temperature of the latter, on the temperature at which the egg was 

 stored prior to its incubation, and even on the age of the hen. It is de- 

 sirable, therefore, if any very specific age of development is required, 

 to start a series of eggs in the incubator at 3- or 4-hr intervals and then 

 fix and mount these at the same time. 



For the removal of the embryos from the egg, there is necessary first a 

 series of finger bowls or any circular glass dishes of 5 to 6 in. in diameter 

 and 2 to 3 in. in depth, a number of Syracuse watch glasses, a large 

 quantity of a 0.9 per cent solution of sodium chloride, a pair of large 

 dissecting scissors, fairly fine forceps, a pipette of the eye-dropper type, 

 some coarse filter paper, and a pencil. 



No very great accuracy is required in making up the normal salt solu- 

 tion, and any percentage between 0.7 and 1 will be sufficient for the 

 purpose in mind. Although it is customarily specified that the temperature 

 of the solution should be 102 to 103° F, anywhere within 10° on either 

 side of these figures is relatively safe. The egg is removed from the in- 

 cubator and placed in one of the finger bowls, which is filled with the 

 warm normal saline solution until the egg is totally immersed. If the 

 operator is rather skilled, it is possible, of course, just to break the egg 

 into the warm saline solution as though one were breaking it into a 

 frying pan, but it is recommended that the inexperienced prepare several 

 hundred wholemounts before they endeavor to do this. The method by 

 which the inexperienced can be assured of getting a perfect embryo on 

 every occasion is first to crack open the air space which lies at the large 



183 



