650 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



individualization there decreases the potentiality of small somatic parts to 

 reproduce the whole organism in an apparently unending series, and corre- 

 spondingly, there decreases the potentiality ito immortal life of these parts. In- 

 stead, this potentiality to immortality becomes dependent entirely on the 

 special mechanism of sexual reproduction, which in the higher organism is 

 of such a kind that at no time are the sex cells exposed to the direct action 

 of the environment. However, certain somatic ceLls and tissues of these dif- 

 ferentiated organisms still retain their potential immortality, as exemplified 

 in the propagation of tumor tissues in succeeding generations of hosts and 

 of embryonal tissues kept in tissue culture ; but in these cases the tissues are 

 able to manifest a potential immortality only if they are supplied with an 

 environment in which the complex substances specifically needed for their 

 growth, as well as other needs, are experimentally provided. They cannot 

 be propagated in the natural inorganic environment, which would be adequate 

 for the propagation of parts of lower organisms. 



In this first circuit of the relationship between organism and environment, 

 the evolution of individuality consisted in the development of an organism 

 which became more and more autonomous, more and more independent of the 

 environment, except that it needed the environment as the source of its food 

 and energy. However, there arose on the basis of and closely connected with 

 this circuit, a second one, in which the evolution went in the opposite direction. 

 Here, the increasing complexity and differentiation of the organism led, on 

 the contrary, to a more intimate interaction between the organism and the 

 environment. This environment became increasingly important and it deter- 

 mined to a large extent the fate of the individual, his ability to maintain 

 himself and to find satisfaction in his world. In this second circuit, organism 

 and environment were connected by way of sense organs, nervous system and 

 muscular system, by means of which the organism acted again on the environ- 

 ment. The evolution of this circuit depended on the refinement of these 

 specific organs and their organ differentials. Thus the organism came into 

 contact with a much more extensive part of its environment and the contacts 

 became more specialized and variegated. An early stage of this development 

 was reached with the production of conditioned reflexes in the interaction 

 between environment and organism. Alterations occurring in the nervous 

 system as the result of repeated stimulation, made it possible that simple 

 environmental factors more or less loosely or accidently connected with the 

 direct stimulus, were able effectively to replace the latter. Furthermore, pic- 

 tures and thoughts, representing environmental factors and systems of such 

 factors, eventually could substitute for the environmental factors and systems 

 themselves and thus determine the mode of reaction of the organism. Thus, 

 conditioned thought reflexes developed. Concomitantly, a great refinement 

 took place in the manner in which the nervous system was affected by these 

 outer and inner factors, and the intracerebral reactions became longer-lasting 

 and more significant. These various changes left important after-effects in 

 the form of memory and thoughts ; analysis and synthesis thus became possi- 

 ble. 



