INFLUENCE OF RADIO-ACTIVITY. 353 



At the close of this period the fauna had reached their greatest 

 physical development with the dawn of psychical processes. The 

 surface of the dry land had undergone great changes from the 

 evolution of the elements, and the deposition of organic material 

 and a varied flora was evolved. Life was divided into numberless 

 genera and species allocated to different locales. 



As before, there was no sharp line of demarcation between the 

 secondary and tertiary periods. The tertiary period might be con- 

 sidered as continued to the present day, and is the period of cumula- 

 tive re-action, as in this form irradiation was effective mainly ; 

 the natural radio-activity has waned further and enormous radio- 

 active screens have developed. The characteristics of this period 

 are the loss of certain radio-active protectives of individuals, the 

 diminution of size, greater vascularity and the development of 

 mentality. 



During this period the necessity for thick dermal coverings 

 as a radio-active shield has gradually declined with the wan- 

 ing of the natural radio activity and were discarded as life with 

 thinner coverings became capable of support, but certain survivals 

 continue to the present day, c.f. elephant, hippopotamus. The 

 constant irritation at all periods of growth also decUned with, pari 

 passu, a decline in the size of the fauna. 



_ The period of life was gradually diminished as the chance of 

 accident to health was increased by the development of greater 

 virulency in the micro-organisms of disease and the increased 

 toxicity of animal poisons, which occurred with the decline of the 

 natural radio-activity. 



The development of greater vascularity, especially in the super- 

 ficies, was rendered simpler. It is proved that excessive radio- 

 activity has the effect of producing intermittent locaUsed constric- 

 tions in the blood vessels, which are naturally more effective in the 

 smaller channels, and the removal from its influence by the decline 

 would promote development. 



The development of mentahty would also be materially aided 

 by the decline, when the results of the experiments of London, 

 Danysz, and others are noted. 



That a certain amount of radio-activity is essential to life 

 seems probable. In the evolution of the elements it seems that 

 those of high atomic weight are evolved first ; the effect of the 

 deposit of such elements on natural radio-activity would be to 

 easily screen off the radiant energy, but at the same time as such 

 reaction takes place the elemental substance itself emits secondary 

 radiant energy, and the intensity of this is directly proportional to 

 the atomic weight. Thus the localities where least radio-activity 

 is present would not be those where the strongest individual ab- 

 sorbent was present, but where vast deposits of elemental substance 

 of low atomic weight occurred sufficient to absorb the natural radio- 

 activity by the thickness of the deposit, and in so doing not emitting 



