Ergosterol (vitamin D)

In-depth study of the so-called. vitamin A showed that this substance consists of two different substances that are not identical to each other either in chemical and physicochemical properties (for example, with respect to thermolability), or in biological effect, or, finally, in their content in various food products ... Fish oil, for example, contains both, but some other fats (butter) contain vitamin A but do not contain this supposed second substance. Regarding the latter, further experiments found that its introduction to young animals, in which a violation of the ossification process, similar to rickets of childhood, was experimentally caused, causes a rapid improvement or even complete disappearance of the pathological process. Therefore, this new substance, isolated from vitamin A under the name "vitamin D", is also called the antirachitic factor. To what extent both the names are correct, we will see below.