﻿CURRENT LITERATURE 



of youthful, in the place of old, protoplasm. However, the new animal is 

 produced, it is found to become young, in its metabolism, as if it came from an 

 egg. Chapter 6 shows that this same process occurs also in agamic reproduc- 

 tion in other forms, such as certain annelids, in protozoa, coelenterates, etc. 



Chapter 7 deals with the artificial control of rejuvenescence apart from 

 reproduction. It is found possible by starving in these animals to bring about 

 dedifferentiation and complete rejuvenescence. By starvation the obstacles 

 to metabolism are removed and the metabolic rate rises to just the same 

 degree as it does in a young individual formed by sexual reproduction. 



In Part III is recorded a very fundamental discovery which has been made 

 the basis of the author's explanation of the attainment of animal forms and 

 the development of a highly elaborated adult from a simple germ, without 



to the number of units or pangenes in it. This fundamental discovery is that 

 of the axial gradient of metabolism, and the dominance and subordination of 

 parts during development in relation to this gradient. The author had found 

 that the head end of an animal, or that part where the nervous system lies, 

 or is to lie, has a higher rate of metabolism than the parts lying behind it. 

 There is in the body of Planar ia, and in other animals as well, a metabolic 

 gradient from before backward, and from the midline toward the sides, and 

 sometimes from back to belly. These are three coordinate axes. The parts 

 which are most active metabolically exercise an inhibitory power on the less 

 active parts in a manner exactly analogous to the control exercised by the 

 growing tip of a plant on the older parts. It is this control of the more rapidly 

 metabolizing parts which controls the development, and differentiation, and 

 dedifferentiation. This conclusion is proved by experiments showing that if 

 in any way the control of the dominant region is removed, the subordinate 

 parts may attain to dominance in their turn and start a new head, and by a 

 resulting reorganization of the materials cause the appearance of a new indi- 

 vidual. The development of any part of" the growing organism is determined 

 by the position the part occupies in its relation to these coordinate axes of 

 metabolic gradients. If, for example, one removes the head, the parts behind 

 it are now released from the inhibition exercised by a more rapid metabolism 

 in front of them, the rate of the anterior margin at once rises and dominates the 

 parts behind, the material is reorganized from this new head and a new indi- 

 vidual produced. This discovery, which is established by a very large amount 

 of experimental observations, enables one to control the processes of regenera- 

 tion and morphogenesis. It explains a vast number of facts of regeneration 

 morphogenesis, teratomas, and so forth, for which there has been hitherto no 

 explanation at all. It is brought into this book because, with the release of 



tion. Animals thus show themselves to be in essentials, so far as their morpho- 



