To solve this problem bits of the heart and blood vessels of a chick embryo were grown. These growths were immersed in salt solution for a few minutes and then placed in the new plasma and it was soon found that thus the tissue could be made to live on indefinitely. Growth is more rapid the earlier the stage of it and it soon declines; hence the advantage of using tissue from embryos. But by subjecting these artificial growths to washings it was found that they were many times greater at the end than at the commencement of the month, showing that they do not grow old at all. Thus C. Pozzi says: The pulsations of a bit of heart which had diminished in number and intensity or ceased could be revived to a normal state by washing and passage through a new solution. In a secondary culture two fragments of heart, separated by a free space, beat strongly and regularly, the larger fragment 92, the smaller 120 times a minute. For three days the number and intensity of pulsations of the two parts varied slightly. On the fourth they diminished considerably in intensity, the large fragment beating 40, the smaller 90 times. When the culture was washed and placed in a new medium, the pulsations again became strong, the larger one 20, the smaller one 60 times a minute. At the same time, the fragments grew rapidly, and in eight hours they were united and formed a mass of which all the parts beat synchronously. Pozzi again says: On January 17 the fragment of a chicken heart embryo was placed in plasma. It grew readily on a thick crown of conjunctive cells. In three days the pulsations, which were regular and strong at the beginning, grew feeble and ceased completely, and this state continued for more than a month. On the 29th of February, the culture, which had been subjected to fourteen passages, was dissected and the central film placed in a new medium. After the fifteenth passage it contracted rhythmically, with pulsations as strong and frequent as on January 17, _viz._, from 120 to 130 per minute. During March and April this fragment of a heart continued to beat from 60 to 120 times per minute. As the growth of the conjunctive tissue became more active, it was necessary, before each passage, to extirpate the new connective tissue formed around the muscle. On April 17 the fragment beat 92 times, agitating all the mass of the tissue and the neighboring parts of the middle of the culture. On May 1 the pulsations were feeble and they were given their thirty-fifth passage. In the manipulation the muscular tissue was stretched and torn so that the contractions ceased.