The dynamics of living matter . dynamicsofliving1906loeb Year: 1906 DYNAMICS OF REGENERATIVE PROCESSES 217 fore arm, the hand, and the leg from the knee down — may suddenly be- gin to grow even if the body had already reached its final size. This phenomenon, known as acromegaly, is comparable to the process of re- generation, inasmuch as the problem in this case is also what causes this sudden growth which normally does not occur. It has been ob- served that this disease is often connected with a degeneration of the hypophysis, a small organ of enigmatic function. An attempt has been made (Vo
The dynamics of living matter . dynamicsofliving1906loeb Year: 1906 DYNAMICS OF REGENERATIVE PROCESSES 217 fore arm, the hand, and the leg from the knee down — may suddenly be- gin to grow even if the body had already reached its final size. This phenomenon, known as acromegaly, is comparable to the process of re- generation, inasmuch as the problem in this case is also what causes this sudden growth which normally does not occur. It has been ob- served that this disease is often connected with a degeneration of the hypophysis, a small organ of enigmatic function. An attempt has been made (Von Cyon) to cure this disease by feeding the patient on normal hypophyses. This idea is based on experiences made in regard to the thyroid gland. Complete extirpation or degeneration of the thyroid gland in growing persons causes a standstill of growth and sexual and mental development. It has been found that if such patients be fed on thyroid glands, the growth and development can be again started. This seems to speak in favor of the idea that the action of specific substances may cause the post-adult growth of arms and legs in the case of acromegaly. It may, however, be a case of growth due to nervous influences com- parable to the experiences of Przibram in Alpheus. 6. The Effect of Some External Conditions upon Regeneration AND THE Transformation of Organs If we cut a piece ah, Fig. 59, from the stem 55 of Antennularia an- tennina (Fig. 60), a hydroid, and put it into the water in a horizontal position, new stems cd, Fig. 59, may arise on its upper side. The small branches on the under side of the old stem ab begin suddenly to grow vertically downward.* In appearance and function these downward-growing elements are entirely dif- ferent from the branches of the normal Antennu- laria; they are roots. In order to understand better the transformation which thus occurs in these branches, it may be stated that under normal conditions they have a limited growth (see Fig. 60), are
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