The distribution of glycogen in chick hearts was studied during incubation and one week following hatching. Concurrent histochemical and chemical studies revealed a gradual increase in the deposition of glycogen during the first half of incubation. During the latter half of incubation the average content of chemically extractable glycogen remained relatively stable until day 19 when a significant decline (p < 0.001) was noted. This decrease was attributed chiefly to the decline in the acid-soluble fraction.
Throughout the incubation period significantly greater (p = 0.05) amounts of chemically extractable glycogen were present in the left chambers and interventricular septum than in the right chambers. These differences were not evident in the post-hatched chick.
Histochemically, glycogen was demonstrated in the chick hearts throughout the incubation period, but no appreciable amount was detected in the hearts one week after hatching. Chemical analysis of the latter revealed that the glycogen content was below the threshold thought to be necessary for its histochemical demonstration.
Parallel decreases noted in both the depth of stain intensity and the acid-soluble fraction serve as further evidence that the acid-soluble fraction is primarily responsible for the histochemical reaction observed with glycogen stains.