284 THE BODY AT WORK 



account for physiological phenomena, this one must be brought 

 to the test by varying the conditions under which impulses pass 

 along nerves, and ascertaining whether the consequent altera- 

 tion in the force, rate, and other attributes of the phenomena 

 are in accordance with physical laws. In applying these tests 

 to the activities of protoplasm, we are, however, met by an 

 insuperable difficulty. The matter which transmits nerve- 

 impulses is alive. We have no laboratory standards by which 

 to judge whether the changes in conduction which are pro- 

 duced by changes in the conditions of the conductor are, or 

 are not, consonant with physical theory. It is with proto- 

 plasm that we are dealing, and not with a mixture of proteins 

 in solution. If we surround a nerve with nitrogen, it loses its 

 conductivity in five hours, to recover it when oxygen replaces 

 the neutral gas. This has been regarded as proving that 

 metabolism of the nerve is necessary for the transmission of 

 impulses. But conductivity is a phenomenon of life. De- 

 privation of oxygen for five hours must bring the nerve-sub- 

 stance to the verge of death. It might be argued that the 

 retention by the nerve for so long a time of its power of con- 

 ducting impulses shows that its metabolism is not a cause of 

 the phenomenon. Again, it has been shown that warming the 

 nerves of cold-blooded animals greatly increases the rapidity 

 of conduction. It is more than doubled in the nerves of the 

 " foot " of a slug and a similar increase has been proved for 

 the nerves of a frog by a rise of temperature of 10 C. Re- 

 flecting on the results of this experiment, a physicist would 

 exclaim : " Then an impulse is a wave of chemical change. A 

 rise of 10 C. increases the rate of chemical processes from 

 two to three times ; whereas no known physical process is 

 accelerated by more than 5 to 15 per cent." But the physiologist 

 remembers that a rise of temperature of 10 C. increases all 

 the activities of a frog. He is hardly prepared to say that 

 its greater vivacity may not be the expression of more rapid 

 oxidation ; but he sees no fore-ordained balance of vital 

 enterprise and chemical change. He is, or ought to be, ex- 

 tremely suspicious of any explanation which appears to over- 

 ride physical laws ; yet, at the same time, he is aware that until 

 he has more accurate knowledge regarding the constitution of 

 protoplasm he will not be in a position to understand how 



