414 THE AMERICAN NATURALIST [Vol. XLII 



of neural physiology, as we know them to-day. It may 

 perhaps prove to be not a finality; but whether in the 

 distant future it be found correct or incorrect, it is from 

 its general standpoint, it seems to me, that the phys- 

 iologist of the present epoch can do his most helpful 

 experimental work. The problem of consciousness 

 should be taken into the physiological laboratory, and the 

 conditions of the manifestation of psychic phenomena 

 should be investigated by laboratory methods. All 

 mental processes, even to the last degree, are dependent 

 on and have their basis in brain processes. The physi- 

 ologist should study in minute detail the cerebral process 

 of each mental act. He can thus inform the psychologist 

 as to the conditions under which psychic phenomena 

 occur. "An individual fact is said to be explained," 

 says John Stuart Mill, ' 4 by pointing out its cause. ' ' And 

 again, ' ' The cause of a phenomenon is the assemblage of 

 its conditions." In this sense the explanation of con- 

 sciousness, it would appear, ought to come, sooner or 

 later, from the physiologists. 



I have spoken of the physiological aspect of other sci- 

 ences. Pathology, the science of disease, or, in other 

 words, perturbed function, is peculiarly close to physi- 

 ology, for there is no sharp line of demarcation between 

 the normal and the abnormal. We may assume the suc- 

 cessive chemical substances involved in a certain progres- 

 sive physiological act to be represented by the series A, 

 B, C, D, in which A is the substance from which the chain 

 proceeds. By analytic and synthetic processes A gives 

 rise to B, B to C and C to D, which is the final end- 

 product of the metabolism. Even with the same quantity 

 of A and the same strength of stimulus, the quantities of 

 B, C and D produced in successive repetitions of the act 

 may vary considerably, owing to unknown factors. It is 



function as pathological. The ('xlitlllility of (IVu.na/be 

 greatly augmented or diminished and still be within the 



