302 E. ROBERTS AND D. G. SIMONSEN 
glutamic acid were the amino acids present in the highest concentrations. Examina- 
tions of extracts of cardiac muscle from Barred Rock chick embryos of between 5 
and 1g days of incubation and from adult chickens of the same strain revealed that 
marked changes take place during the period of development. Figs. 76-79 illustrate 
the patterns observed on chromatograms of cardiac muscle of 14-, 16- and 17-day 
chick embryos and of the adult chicken, respectively, changes being noted in a 
number of the detectable constituents. Valine and hydroxyproline were detected 
in the embryo hearts, but the latter amino acid decreased below the level of detec- 


mo rw | 
Figs. 80-82. Chromatograms of extracts (75 mg samples) of brain of a 16th-day fetal mouse, 
1-day old mouse and an adult mouse, respectively (Figs. 80-82) ; y-Aminobutyric acid, 22, and the 
unlabeled arrows. 
tion in extracts of hearts of adult chickens. The extracts of the adult chicken heart 
showed larger amounts of glycine, serine, valine and the leucines than were found 
in the mouse and rat hearts and the hearts of other mammalian species. 
Figs. 80-82 show chromatograms of extracts of brain obtained from a 16-day 
fetal mouse, 1-day-old mouse and an adult mouse, respectively. On examination of 
a large number of brains from mice of intermediate ages, it was found that the 
content of GABA increased progressively with age up to approx. 30 days after 
birth. The progressive increase in content of GABA with development is also illus- 
trated on the chromatograms (Figs. 83-86) from extracts of pooled brains of tad- 
poles and adult bullfrog. Patterns of amino acids in the bullfrog tadpole, 7 cm long 
(Fig. 85), and at subsequent larval stages were similar to those found in the adult 
bullfrog. Taurine was noted only in the brain of the adult frog, none being present in 
the earlier stages (Fig. 86). Examples of chromatograms prepared from tissues of a series 
of chick embryos at all stages between 4 days of incubation and hatching are shown 
in Figs. 87-g0. GABA was first detectable in the brain of the chick embryo on the 
4th day of incubation (Fig. 87) and increased in concentration with the increasing 
References p. 348/349 
