Activities of two enzymes of the de novo pyrimidine biosynthetic pathway, aspartate transcarbamylase and dihydro-orotase, and one enzyme of the salvage pathway, uridine kinase, were assayed in the liver, heart, brain, and intestine during embryogenesis of the chick, to assess the relation of these pathways to cellular proliferation and organ growth. As the period of embryogenesis ended, the increment of cellular proliferation, as determined by changes in amount of DNA, of liver, brain, and heart decreased, while that of intestine remained relatively constant. The most elevated activities for both enzymes of the de novo pathway were observed in the earliest stages of development, decreasing thereafter with age. These two enzymatic activities changed synchronously in each of the tissues studied. In each organ, the highest activities of the de novo pyrimidine biosynthetic enzymes were coordinated with the stage of most rapid rate of cellular proliferation. In addition, the enzymatic patterns during development paralleled the overall growth rates of different organs. The activity of uridine kinase increased throughout embryonic development in the organs investigated, in contrast to the activities of the enzymes of the pathway of de novo pyrimidine biosynthesis. Speculation

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The findings of both studies suggest that the interaction between student gender and SP gender, unconfounded by case content, had no effect on the students' scores and ratings.

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