In recent experiments 24–32 hr. chick embryos were treated with saline extract of adult chicken brain, which was injected into the yolk, into the sub-blastodermal space, or deposited over the blastoderm. After an additional 60-hr, incubation period, 30 to 40 per cent of the surviving embryos showed defects of the brain, spinal cord and eye, such as anencephalus, microcephalus, abnormal shape of the brain vesicles, rachischisis, anophthalmia and microphthalmia (Lenicque, 1959; Clarke & McCallion, 1959; Braverman, 1961). In addition, a number of embryos showed abnormal proliferation in the walls of the brain vesicles.

When other tissue extracts were examined it was found that the abovementioned abnormalities could be produced only by saline extracts of chick brain and nervous retina, and not by extracts prepared from liver, spleen and skeletal muscle. The latter extracts do sometimes affect brain development, but then always in association with defects in other organ systems.

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