THE WORLD'S CONSERVATION PROBLEM 167 



have the capacity of picking up sound waves of a much higher pitch than 

 those which impress our duller senses, while the greater acuity of vision 

 of birds, the keener sense of smell of various animals, the delicacy of 

 perception of fishes for changes in pressure, are facts that are too well 

 known to need repetition. To a certain extent these great differences 

 in sense perception are directly referable to peculiarities in structure. 

 The same fundamental system of construction characterizes the ner- 

 vous system of the entire animal kingdom. The structural unit is the 

 nerve-cell and nerve-fiber. The greater the number of these cells and 

 fibers the greater is the complexity of the nervous system. Some of the 

 cells are designed to pick up and transfer to the distributing apparatus 

 the stimuli for which the organs are attuned. In addition to the re- 

 ceiving apparatus there is the transformer and elaborator of the incom- 

 ing impulses, and finally there is the discharging apparatus as repre- 

 sented by the organs of locomotion, speech and. others, which express 

 objectively the sum total of the animal's activities. Already science has 

 taught us something about the nature of that mysterious nervous im- 

 pulse upon which thought, action and life depend. In fact there is a 

 similarity between the rhythmic character of the life processes and the 

 rhythmic discharges of certain types of cells in a battery. Here, as in 

 all other enquiries which concern the energies of living matter, we are 

 led back to the study of the cell. The millions of cells composing our 

 bodies have certain common characteristics. The central portions are 

 probably the parts most immediately related to the production of energy, 

 while the external layers govern the taking in or throwing off of sub- 

 stances by the cell. A theory in regard to the manner in which anes- 

 thetics act attributes an important role to this external layer, as the 

 place where .the actual physico-chemical changes take place that re- 

 sult in anesthesia. The effects depend to a certain extent upon the 

 presence in this outer envelope of certain fat-like substances which, 

 combining with the enhaled ether or chloroform, produce loss of con- 

 sciousness. There are also reasons for believing that in this same ex- 

 ternal layer of the cell the nerve impulse is generated, depending upon 

 changes akin in their manifestation and mode of origin to those giving 

 rise to electrical disturbances. One of the greatest services yet rendered 

 biology by physical chemistry is the presentation of the facts suggest- 

 ing that the regulation of the production of nerve impulses is not de- 

 pendent upon some vague mysterious vital force, but is probably com- 

 parable to those phenomena called by the chemists "reversible reac- 

 tions." The mixture of two substances may be followed by a chemical 

 reaction in which the two original substances are in part decomposed, 

 forming new chemical compounds. At a certain point this reaction 

 ceases, as an equilibrium has been established, and then only after the 

 balance has again been disturbed is the decomposition completed or a 



