
The SciencesDecember 1, 1970
Rickets
Although it is still widely regarded as a dietary-deficiency disease resulting from a lack of "vitamin D," it results in fact from a lack of sunlight. In smoky cities it was the first air-pollution disease

Rickets
Although it is still widely regarded as a dietary-deficiency disease resulting from a lack of "vitamin D," it results in fact from a lack of sunlight. In smoky cities it was the first air-pollution disease

The Sex Gas of Hydra
Usually this small animal reproduces by budding, but it can also develop male and female organs for sexual reproduction. What factors determine which method of reproduction it uses?