6 DYNAMICS OF LIVING MATTER 



forms of tropisms in the same individual, and to the changes of these 

 tropisms under the influence of internal and external factors. In 

 these lectures we shall discuss some of the elementary tropisms and 

 their role in the animal instincts and in the preservation of the indi- 

 vidual and the species. 



The will actions of animals, i.e. those motions which are executed 

 consciously, will not be discussed here as I have already analyzed them 

 in another book.* I will simply state here that I consider conscious- 

 ness the function of a definite machine or mechanism, which we may 

 call the mechanism of associative memory. Whatever the nature of 

 this machine may be it has one essential feature in common with the 

 phonograph, namely, that it reproduces impressions in the same chrono- 

 logical order as that in which they were received. The mechanism of 

 associative memory seems to be located - - in vertebrates - - in the cere- 

 bral hemispheres. It follows from the experiments of Goltz that one of 

 the two hemispheres is sufficient for all the phenomena of memory and 

 consciousness. As far as the chemical or physical mechanism of memory 

 is concerned, we have at present only a few vague data. H. Meyer 

 and Overton have pointed out that substances which are easily soluble 

 in fat are also, for the most part, strong anaesthetics, e.g. ether, chloro- 

 form, etc., and that the ganglionic cells are especially rich in lipoids. 

 It is possible that the mechanism of associative memory depends in 

 part upon the properties and activities of the fatty constituents of the 

 cerebral hemispheres. Another fact which may be of importance is 

 the observation of Speck that if the partial pressure of oxygen in the 

 air is lowered to below one third of its normal value, the fundament 

 of mental activity, namely, memory, is almost instantly interfered with, 

 and total loss of consciousness rapidly follows. 



In those animals which possess the mechanism of associative memory, 

 a number of the automatically regulated processes may become con- 

 scious. Respiration is purely an automatic process, yet we may at any 

 time become conscious of it. This has misled a number of authors 

 to believe that such automatic processes as in ourselves may become 

 conscious must be accompanied by consciousness in any animal in which 

 they occur. These authors overlook the fact that the automatic mech- 

 anisms of self-preservation must occur in every organism, while an 

 apparatus for associative memory may be found only in a limited num- 

 ber of organisms. Without such an apparatus, consciousness is impos- 

 sible. The fact that a physiological process may become conscious 

 in ourselves does not therefore prove that it is accompanied by conscious- 

 ness in every organism. 



* Loeb, Comparative Physiology of the Brain and Comparative Psychology. G. P. Put- 

 nam's Sons, New York. 



