38 THE ACTIVE FORCES OF LIVING ORGANISMS 



increased. But this increase in oxygen pressure is 

 accompanied by a decrease in carbonic-acid pressure, 

 due to the negative pressure in the veins. Meta- 

 bolism must therefore possess a rhythmical character ; 

 moreover, it is not improbable that as the blood- 

 pressure rises and falls with the respiratory move- 

 ments, the tissues also expand and contract. Thus, 

 when arterial pressure has attained its maximum at 

 the beginning of expiration it seems likely that the 

 transfer of oxygen to the tissue, which may then be 

 supposed to take place, is accompanied by a certain 

 degree of expansion. Indeed, unless we imagine 

 some such movement to occur in the nerve-cells, it is 

 difficult to conceive how the molecular and chemical 

 action going on in them can govern the metabolic 

 processes taking place in the tissues. However this 

 may be, it will be seen that, so long as respiration 

 continues, molecular movements and ethereal vibra- 

 tion never cease in the nervous system and tissues 

 generally, so that even in the deepest sleep there are 

 forces at work which determine the mode in which the 

 building up of raw material into new molecules shall 

 take place. But though the respiratory movements 

 and the influence of nervous vibration upon the 

 tissues may be regarded as contributory causes in the 

 formation of new molecules, yet the facts that meta- 

 bolism will go on in the stomach after most of the 

 nerves to that organ have been cut, and that growth 

 in the case of the hair and nails will continue after 

 death show that chemical action, the ether and 



