Abstract
In a previous article I had shown that rhythmical muscular contraction as it occurs in fragments or the whole hearts of embryos in simple hanging drop cultures is regular only for a few hours. After this it becomes irregular; there are periods of activity followed by periods of rest. These active periods are ushered in by rapid strong contractions which gradually become less and less forcible and rapid until they finally cease. After a shorter or longer rest period of several minutes, the contractions begin again, as before.
These irregularities I had long ago concluded were due to the accumulation of waste products about the contracting cells. In the simple hanging drop cultures the only means of escape of such substances is by diffusion into the outer portion of the hanging drop of medium. I prepared at that time a culture 1 which allows one to wash continuously a greater part of such hanging drops of plasma with a stream of serum. The serum in this apparatus is dropped at the rate desired on the upper end of a wick which passes to the hanging drop and then into a receiving chamber. In the hanging drop on the surface of a cover glass the fibres of the wick are teased apart so that they transverse all parts of the hanging drop. The fragment of tissue or cells to be tested is placed in the center of the hanging drop. Plasma is used as the medium for the hanging drop. It is allowed to clot before the stream of serum is started.
In such cultures I found that as the serum is passing the contractions of the heart become regular and forcible in those cells which are sufficiently separated to be well washed by the serum.
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