GROWTH OF TISSUES OF THE CHICK EMBRYO 67 



The muscle plates were dissected out in a somewhat similar 

 manner. The skin and the surrounding tissue were removed and 

 the muscle plates were cut free from the neural tube with sharp 

 scissors. 



The piece of tissue to be transplanted was taken from the 

 Ringer's solution with a small sterile pipette and dropped with 

 the solution on the surface of the cover glass. Excess of Ringer's 

 solution was removed with the pipette and a drop of the plasma 

 run over the specimen. The cover glass was then either immedi- 

 ately inverted over the hollow slide or the slide placed over 

 the surface of the cover glass, depending on the position desired 

 for the specimen in the drop; the specimen settled always to the 

 lower surface of the drop. The cover glass was then sealed to 

 the slide with paraffin. Clotting took place at once before the 

 slide could be transferred to the incubator. The time occupied 

 for the entire dissection and mounting was five minutes. 



The preparation of blood plasma 



Oxalated plasma. In the earlier work on chicks, some difficulty 

 was encountered in the preparation of a pure plasma which could 

 be preserved for sufficient time to allow for the dissection of the 

 specimens. In searching for an agent which prevents coagulation, 

 sodium oxalate was selected as the most suitable. 



The blood was removed with a pipette from the heart of a chicken 

 to a test tube containing 1 per cent sodium oxalate solution. Suf- 

 ficient blood was added to make the concentration of the sodium 

 oxalate 0.1 per cent. The tubes were then centrifugalized and the 

 clear plasma removed with a pipette and placed on ice until 

 ready for use. 



For using this plasma, quantitive estimates were necessary for 

 the precipitation of the sodium oxalate with calcium chloride and 

 for the correction of the excess of the sodium chloride resulting 

 from this chemical change. The precipitation was made, as the 

 drops were used, in a pipette graduated to one part in ten or one 

 part in five, depending on the dilution of the plasma desired. The 

 quantity of calcium chloride necessary to precipitate the sodium 



