2 LIBBIE H. HYMAN. 



I. GENERAL DISINTEGRATION GRADIENTS IN THE CHICK. 



In this section of the paper the disintegration gradients of 

 all observable parts of the chick embryo except the heart will 

 be described. The heart will be treated in a separate paper. 

 The observations deal almost wholly with ectodermal and meso- 

 dermal structures as entodermal structures cannot be seen 

 clearly enough to enable one to determine the time or course of 

 death in them. 



i. Method. The yolks were poured out into physiological salt 

 solution (0.9 per cent.) warmed to 40 C., and the embryo 

 removed as usual to a watchglass. The salt solution was then 

 withdrawn whereupon the blastoderm with the embryo flattens 

 out upon the bottom of the watchglass. An oval ring, its central 

 opening about the size of the area pellucida, was then cut out of 

 hard filter paper, and lowered on the blastoderm, so that the 

 embryo occupied the center of the opening. By this simple 

 method the blastoderm is held flattened. The watchglass was 

 then rilled with the desired killing agent made up in 0.9 per cent, 

 salt solution warmed to 40 C. In most cases the whole was 

 then covered with a thin circular piece of glass with the exclusion 

 of air bubbles. In other cases the watchglass was left uncovered. 

 The death of the embryo was then watched under the low power 

 of the compound microscope. The preparation was kept warm 

 by placing it from time to time on a heated object. 



Special care is necessary in removing very young embryonic 

 stages from the yolk, for the blastoderm tears easily and further 

 both the albumen and yolk are strongly adherent to the blasto- 

 derm. It was found necessary to proceed as follows in such cases. 

 After emptying the yolk under salt solution, the albumen was 

 completely dissected off leaving the yolk intact. A cut was 

 then made around the blastoderm and by manipulating the cut 

 edge the vitelline membrane was picked up and peeled off leaving 

 the blastoderm still on the yolk. The point of a forceps was 

 then passed beneath the blastoderm freeing it from the yolk. 

 The blastoderm could then be floated off into a watchglass. 

 The blastoderm is freed from adherent yolk by rocking it in 

 several changes of salt solution. 



The killing agents used were potassium cyanide, ammonium 



