ADDRESS. 29 



ha3 not been wound, these relations can be re-established — the process of 

 life re-awakened — by the application of the required stimulus. 



I was also desirous to illustrate the relation between physiology 

 and its two neighbours on either side, natural philosophy (including 

 chemistry) and psychology. As regards the latter I need add nothing 

 to what has already been said. As regards the foi-mer, it may be well 

 to notice that although physiology can never become a mere branch of 

 applied physics or chemistry, there are parts of physiology wherein 

 the principles of these sciences may be applied directly. Thus, in the 

 beginning of the century, Young applied his investigations as to the move- 

 ments of liquids in a system of elastic tubes, directly to the phenomena 

 of the circulation ; and a century before, Borelli successfully examined the 

 mechanisms of locomotion and the action of muscles, without reference to 

 any, excepting mechanical principles. Similarly, the foundation of our 

 present knowledge of the process of nutrition was laid in the researches 

 of Bidder and Schmidt, in 1851, by determinations of the weight and 

 composition of the body, the daily gain of weight by food or oxygen, the 

 daily loss by the respiratory and other discharges, all of which could be 

 accomplished by chemical means. But in by far the greater number of 

 physiological investigations, both methods (the physical or chemical and 

 the physiological) must be brought to bear on the same question — to co- 

 operate for the elucidation of the same problem. In the researches, for 

 example, which during several years have occupied Professor Bohr, of 

 Copenhagen, relating to the exchange of gases in respiration, he has 

 shown that factors purely physical — namely, the partial pressures of 

 oxygen and carbon dioxide in the blood which flows through the pul- 

 monary capillaries — are, so to speak, interfered with in their action by the 

 ' specific energy ' of the pulmonary tissue, in such a way as to render this 

 fundamental process, which, since Lavoisier, has justly been regarded as 

 one of the most important in physiology, much more complicated than we 

 for a long time supposed it to be. In like manner Heidenhain has proved 

 that the process of lymphatic absorption, which before we regaided as 

 dependent on purely mechanical causes — i.e., differences of pressure — is 

 in great measure due to the specific energy of cells, and that in various 

 processes of secretion the principal part is not, as we were inclined not 

 many years ago to believe, attributable to liquid diffusion, but to the same 

 agency. I wish that there had been time to have told you something of 

 the discoveries which have been made in this particular field by Mr. 

 Langley, who has made the subject of 'specific energy' of secreting-cells 

 his own. It is in investigations of this kind, of which any number of 

 examples could be given, in which vital reactions mix themselves up with 

 physical and chemical ones so intimately that it is difficult to draw the 

 line between them, that the physiologist derives most aid from what- 

 ever chemical and physical training he may be fortunate enough to 

 possess. 



