Note on the production of acid by tissues growing in vitro

Abstract

Connective-tissue cells of the chicken, growing in vitro in chicken plasma to which a little blue litmus has been added, produce rapidly a focal, pink coloration of the medium. If a number of small fragments of one tissue (heart muscle or the aorta of young chicks, or chicken sarcoma) be plated out with the plasma medium in a petrie dish, it will be found that all the tissue bits are at first stained blue, but that those from which growth occurs become pink, while the growing tissue itself is unstained. The fragments remaining permanently inert keep the blue color.

Often a pink coloration of tissue bits can be observed at a time when growth is found, microscopically, to have barely started. The acid change is in general sharply localized to the neighborhood of the growing tissue. When growth is checked by placing the preparation in the ice-box, neutralization in the acid foci is often incomplete at the end of forty-eight hours, and this even when the bulk of alkaline plasma is relatively large and its plasma network thinned by dilution. Diffusion in the plasma medium as thus indicated is very slow. Under the ordinary circumstance of in vitro life without artificial provision for a circulation of fluid, tissue proliferation must take place almost from its beginning, in an acid medium. This constitutes a serious fault in the method of cultivation.

The nature of the acids produced by the growing tissue has not been determined. Carbonic and lactic acids are presumably present in greatest quantity. That the amount of acid formed may be very considerable has been shown by titrating out the as yet unclotted blue plasma to the tint acquired by the tissue cultures.