20 BIOLOGY 



hemispheres, as the experiments of Goltz have shown. The same 

 author has shown, moreover, that one of the two hemispheres suffices 

 for the efficiency of this mechanism and for the full action of con- 

 sciousness. As far, however, as the physical or chemical character of 

 the mechanism of memory is concerned, we possess only a few starting 

 points. We know that the nerve cells are especially rich in fatty con- 

 stituents, and Hans Meyer and Overton have shown that substances 

 which are easily soluble in fat also act as very powerful anaesthetics, 

 for instance, chloroform, ether, and alcohol, and so on. It may be 

 possible that the mechanism of associative memory depends in some 

 way upon the constitution or action of the fatty compounds in our 

 nerve cells. Another fact which may prove of importance is the obser- 

 vation made by Speck that if the partial pressure of oxygen in the air 

 falls below one third of its normal value, mental activity very soon be- 

 comes impaired and consciousness is lost. Undoubtedly the unravel- 

 ing of the mechanism of associated memory is one of the greatest dis- 

 coveries which biology has still in store. 



VI. Elementary Physiological Processes 



It is, perhaps, possible that an advance in the analysis of the me- 

 chanism of memory will be made when we shall know more about 

 the processes that occur in nerve cells in general. The most elemen- 

 tary mechanisms of self-preservation in higher animals are the respira- 

 tory motions and the action of the heart. The impulse for the respira- 

 tory action starts from the nerve cells. As far as the impulses for the 

 activity of the heart are concerned, we can say that in one form at 

 least they start from nerve cells, and in all cases from those regions 

 where nerve cells are situated. But as far as the nature of these im- 

 pulses is concerned we know as little about the cause of the rhythmi- 

 cal phenomena of respiration and heart-beat as we know concerning 

 the mechanism of associative memory. It is rather surprising, but 

 nevertheless a fact, that physiology has not progressed beyond the 

 stage of mere suggestions and hypotheses in the analysis of such 

 elementary phenomena as nerve action, muscular contractility, and 

 cell division. Among the suggestions concerning the nature of con- 

 tractility those seem most promising which take into consideration 

 the phenomena of surface tension. The same lack of definite know- 

 ledge is found in regard to the changes in the sense organs which give 

 rise to sensations. It is obvious that the most striking gaps in bio- 

 logy are found in that field of biology* which has been cultivated 

 by the physiologists. The reason for this is, in part, that the analysis 

 of the elementary protoplasmic processes is especially difficult, but 

 I believe that there are other reasons. Medical physiologists have 

 confined themselves to the study of a few organisms, and this has 



