INTRODUCTION 9 



ardent advocate of the essentially chemical nature of 

 such reactions. 



The foregoing illustrations well illustrate the essen- 

 tially chemical nature of the mechanisms for corre- 

 lating the activities of living systems. Any marked 

 change induced in an organism must of necessity inter- 

 fere with such a correlating mechanism and hence 

 give rise to abnormal responses. Hence a pathological 

 state results. In the root tip experiments cited above, 

 we have seen that simple mechanical pressure and the 

 application of a caustic chemical elicit the same re- 

 sponses. Similarly Loeb (1924), in his experiments 

 on the regeneration of Bryophillum colycinum, has 

 shown that mutilation and illumination of the leaves 

 both result in the liberation of various soluble sub- 

 stances which appear to stimulate the growth of the 

 plant. Such experimental results as these offer evi- 

 dence that divers stimulating agencies may be causa- 

 tive of the same response. 



For some thirty years the writer has argued that 

 the apparent stimulating and repressive activities of 

 various physical and chemical agents, as well as the 

 pathological changes which they induce, are due to 

 a common cause, — the release by the cells themselves 

 of a substance capable of modifying cellular activity. 

 For purposes of convenience in discussion, the author 

 has termed this important substance cytost. 



Although the author developed his concept of cytost 

 on the basis of experiments conducted in his labora- 

 tory, the underlying idea is by no means new. Indeed, 

 a similar conception dates back to early antiquity, as 

 recently shown by Professor Breasted (1930) in his 

 study of the Edwin Smith Surgical Papyrus; for it is 



