Abstract
The embryological basis of spina bifida and the associated doubletailed condition has received a number of explanations. Hertwig 1 advanced the basic theory that the bifid condition results from inhibition of gastrulation which retards closure of the blastopore and thereby prevents fusion of the anlagen of the axial organs located on either side of the blastopore. Berge 2 followed Hertwig, attributing bifid tails to a persisting blastopore which mechanically blocks the tail anlagen. Baldwin, 3 studying the effects of ultraviolet irradiation upon frogs′ eggs, concluded that the essential factor was injury to the highly susceptible yolk material (endoderm), which serves as a barrier to the approximation of the blastoporal lips. Bellamy 4 suggested inhibition of the dorsal blastoporal lip, which is a region of high susceptibility to a variety of noxious conditions.
This study is a preliminary report of attempts to determine whether injury to one or more specific regions of the egg is responsible for the bifid condition of the lower back and tail, or whether it is produced by general injury to the egg. Localized sublethal injuries were produced easily by means of ultraviolet irradiation.
A cold quartz burner∗ was used whose spectrograph shows a high proportion of rays at 2537 A. U. The intensity was such that after irradiating early gastrulae for 13 minutes there was no trace of a neural plate within 24 hours. Most of the egg-jelly was removed with scalpels. The eggs were placed in a chamber the bottom of which was a quartz plate 1.65 mm thick. Irradiation was from below, with the ultraviolet burner 2.5 mm from the lower surface of the quartz plate. Shields cut from tinfoil were applied closely to the surface of the egg to protect all except the irradiated region.
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