
Neuman, et al. (1956) injected White Leghorns at 96 
hours of incubation with varying amounts of semi-carbazide,. 
Doses in excess of 3 mg. killed the embryo. Doses of 2.35 mg. at 
4 days caused shortened and malformed lower beak, and a bending 
of the tarsometatarsal and tiblotarsal bones. ‘The suspected 
mode of action was an inhibition of diamine oxidase and perhaps 
other enzymes responsible for deamination. The resulting effects 
were relative to the doses and the developmental stage at which 
the drug was administered. A summary of these experiments is 
reproduced in Table #2. 
Landauer (1953) demonstrated a relationship between 
the stage of development at which the dose was delivered and 
the resulting effect. Insulin administered at 84,120 and 160 
hours in doses of 2 units yielded an overeall effect of a uni- 
form shortening of the embryo. However, the effects were greater 
when administered at the earlier stages of development. 
Syndactylism -was produced in greatest incidence at 84 hours. 
Neuman (1956) demonstrated that the administration of 
semi~carbazide was subject to "a sensitive stage of develop- 
ment (after which a decreasing number of lethalities and ab~ 
normalities were produced". Administration yielded distortion 
and irregularities with twisted legs and beaks. If administered 
at 12 days, the embryo developed normally. 
4, Other chemical factors. 
There are other chemical inhibitory agents the ef-+- 
fects of which have not been linked to mutant gene expression 
either because of lack of knowledge of such a gene or because 
the chemical acts upon the cells directly. Among these are 
compounds classified as antimetabolites which can be further 
subdivided according to their suspected mode of action either 
as analogues of purines, or of amino acids, or of vitamins. 
Waddington (1958) and Friar and Woodside (1956) 
wound that 8-azaquanine when injected into the egg caused re- 
tardation of the whole embryo, especially of the brain and eye 
cups, a retardation of the somite formation and the lack of 
formation of well-defined blood vessels. The chemical varied 
in its effects at various developmental stages and according to 
the relative amounts administered. Both azahypoxamine and 8- 
azaquanine at 0.1 per cent arrested cells in early prophase, 
Benzimidazole at 18 hours and 0.5 per cent produced slight 
cellular degeneration in the newly formed mesoderm and an in- 
hibition of the head region growth. 
Another purine analogue, Leazaserine, when injected 
(0.20 mg.) into 4<dayeold embryos produced skeletal abnormali-~ 
ties, eye defects, and three types of beak defects Dagg (1955). 
Twelve=day embryos showed no skeletal defects when injected with 
the same amount. LD59 studies showed that the dose tolerance 
40 
