142 KERATIN AND KERATINIZATION 



of a system to the part controlled by the signal, the possibility of oscillations 

 arises (p. 143). Weiss and Kavenau believe these will arise, for example, 

 when organs regenerate after partial removal. These may be manifested 

 also at the cellular level and possibly account for some of the fluctuations 

 in cellular activity commonly noted (see also p. 148). 



Fig. 58. Further aspects of Weiss' theory of intercellular control by the 

 exchange in inhibitor molecules. Two kinds of differentiated cells are 

 distinguished by their differentiated products, open circles and triangles. 

 Two kinds of inhibitor molecules, black circles and triangles, are released 

 into the common humoral pool. The rate of production of the two kinds 

 of products is controlled specifically by concentration of their specific 

 products in the pool (reproduced by permission). 



In its present state of development the theory does not give a place to 

 interactions between different cells, which are probably in part effected by 

 the exchange of samples of the differentiated mass, and thus does not 

 attempt to account for the appearance of differentiation and its main- 

 tenance. A differentiating system can be devised, following Rose (1952) if 

 one supposes that the inception of a certain reaction in one group of cells 



