GLYCOGEN IN THE CHICK EMBRYO. 



H. JEANETTE ALLEN, 

 UNIVERSITY OF CINCINNATI. 



In his paper, "Glycogen in the Nervous System of Verte- 

 brates" 1 Gage has pointed out that glycogen is not found in 

 such great abundance in the organs of the chick at any one period 

 of its development as in the embryonic organs of many other 

 forms, including mammals; from which the inference is at once 

 drawn that this difference is correlated with the nature of develop- 

 ment in the hen's egg, where the yolk furnishes an abundant 

 supply of food, available at any moment for the needs of the 

 embryo. The development of the various organs is a gradual 

 one as compared with that of forms which are provided with less 

 yolk, and glycogen, the builder of tissue and energy producer, 

 appears only as it is needed in the successive stages. 



This is particularly striking when comparing the chick with 

 such forms as Petromyzon and Amblystoma, studied by Gage. 

 When contrasted with mammals the same explanation is not 

 as valid, for the mammalian tissue is also able to develop gradu- 

 ally, calling upon the maternal supply when necessary. However 

 it may be supposed that in mammals the embryo is less directly 

 in contact with ts food supply than in the chicken. A great 

 amount of glycogen could not be produced as quickly when a 

 demand arose in tissue development, and consequently a greater 

 supply is produced and maintained in the embryonic tissue itself. 



The following observations in regard to the occurrence and 

 distribution of glycogen in the tissue of the chick, from primitive 

 streak stages to the age of about ten days, are based on material 

 which was fixed and stained according to the methods given in 

 Gage's article, and in all cases the presence of the glycogen has 

 been verified by testing the sections with saliva, according to 

 Gage's directions. 



It gives me pleasure to be able to acknowledge my great 



1 Jour. Contp. Neur., Vol. 27, No. 4. 



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