Burrows: Study of Body Cells. 489 



THE CONTRACTING HEART MUSCLE CELLS. 



The isolated contracting heart-muscle cells which occasionally 

 develop in these cultures from cells migrating from the fragments 

 contract with a rhythm like that of the whole hearts or fragments 

 of the heart transferred to the cultures. Since they occur most 

 infrequently, contracting fragments have been used chiefly for this 

 study. 



The rhythm of the fragments and the whole hearts of younger 

 embryos may never cease when transferred from the chick embryo 

 to the medium. If it does it commences at once again as soon as 

 the temperature for it is restored. During the first few minutes 

 or hours this rhythm is regular; and in the case of the whole hearts 

 and fragments of the ventricle, it is the same as that which occurs 

 normally in the body. After a short time, however, it becomes 

 irregular. There are periods of activity followed by periods of 

 complete rest. These periods of activity, as I have previously de- 

 scribed them, are ushered in by rapid, strong contractions. These 

 contractions gradually decrease in amplitude and rate to the period 

 of complete rest. After a short rest period the active rhythm again 

 intervenes, and so on; their irregular rhythm may continue for as 

 long as eight or nine days in a single hanging drop. 



This slowing of the rhythm and rest, I concluded, was due to the 

 temporary accumulation of waste products, the temporary lack of 

 nutrient substances, or both. After these waste products had slowly 

 diffused away and nutrient substances had moved in, the heart 

 became active again. To prove this I placed several such fragments 

 in a specially devised culture chamber. This chamber was arranged 

 so that serum could be made to flow continuously along a cotton 

 wick, the fibers of which transversed the layer of plasmatic medium. 

 By this means it was possible to continuously wash the medium 

 about the fragment. This culture has been called the ''wick cul- 

 ture."-^ In such cultures the rhythm of the fragments remains 

 regular during the time the serum is flowing, and this regular rhythm 

 continues often for many days or until the protoplasm of the cells 

 is otherwise destroyed by infection, etc. A careful comparison of 

 the irregularities in the case of the contracting heart-muscle cells 

 with those of the migrating ones shows interesting differences. In 

 the case of the migrating and growing cells there are no intermittent 

 rest periods. Migration commences after a latent period. It con- 

 tinues actively for a time; then gradually ceases. In the same cul- 

 ture there is no second recovery period. 



