
increased with the age of the embryo, from 0.10 mg. at 0 to 2 
days to 2.40 mg. injected at 12 days. Blattner et al. (1958) 
inhibited hatching by injecting 0.5 mg. into the blastoderm 
region of the egg. The probable mode of action is interference 
with adenine metabolism. | 
Quanazolo was tested on White Leghorn chickens by 
Younger et al. (1950). The general effects noted were a re- 
duction of Vascularization and of development of the chorioal- 
lantoic membrane, abnormalities of the beak and inhibition of 
feather formation. A dose-effect response was noted with the 
percentage mortality decreasing with decrease in doze (0.5 meg., 
100 per cent mortality; 0.06 mg., 43 per cent mortality). 
Sparingereaction studies demonstrated that the purine affected 
was probably quanine. 
Amino acid analogues have also been tested for possible 
inhibitory action. Among those found to be most effective 
through direct application to the embryo either in the egg or 
as an explant were derivatives of analine and glycine. Herrman 
(1953) treated explanted chick embryos at the 6 somite stage 
with the following analogues, Be2 thienylananine and para- 
chlorophenylalanine were found to produce the most extensive 
abnormalities and to increase the mortality. <A general re- 
tardation of growth, a zigzag neural tube and an irregularly 
formed brain were the most common abnormalities produced. Two 
aliphatic amino acids did not have as pronounced effects on the 
central nervous system as did the above mentioned benzenoid 
compounds. They did, however, produce a general inhibition of 
growth. 
Five other derivatives of alanine and glycine, 
antagonists of leucine and methionine, were tested by Herrman 
(1955) om chick explants. Injection into the yolk sac and onto 
the chorioallantoic membrane of x-bromoallyglycine and we 
bromoallylglycerine produced suppression of somite segregation 
at dose levels of 0.1 mg. Increased effects were found to 
occur at higher concentrations. 
The mode of action for all the foregoing compounds as 
suggested by their structural resemblance to amino acids, was 
probably that of interference with protein synthesis. 
Herrman (1953,1955) and Feldman and Waddington (1955) 
demonstrated that the aliphatic amino acids caused the failure 
of segmentation of the mesoderm, hence the appearance of 
"blocks of unsegmented somites". The aromatic amino acids pro- 
duced retarded growth, increased percentage of abnormalities 
and increased percentage mortality. 
Another fertile field of investigation has been the 
vitamin analogues and nucleic acid antagonists. Blackwood and 
Shorb (1958) studied certain benzimidazoles and benezenes some 
of which were natural moieties of vitamin Bio. Two strains of 
42 
