BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 461 



noiiieiia of the ciiculatioii; and a centiiiy before, Dorelli successfully 

 exaiuiued tlie inecLauisiiis of locomotion and the action of muscles, 

 without reference to any, excepting mechanical principles. Similarly, 

 the foundation of our present knowledge of the j)rocess of nutrition was 

 laid in the researches of Bidder and Schniidt, in 1851, by determina- 

 tions of the weight and composition of the body, the daily gain of 

 weight by food or oxygen, the daily loss by tbe 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 Prof. 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 pulmonary 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 Ileidenhain has j)roved that 

 the process of lymphatic absorption, which before we regarded 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 partis 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 some- 

 thing of the discoveries which have been made in this particular field 

 by IVIr. 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 whatever chemical and physical training he may be 

 fortunate enough to possess. 



There is therefore no doubt as to the advantages which physiology 

 derives from the exact sciences. It coidd scarcely be averred that they 

 would benefit in anything like the same degree from closer association 

 with the science of life. Nevertheless there arc some points in respect 

 of which that science may have usefully contributed to the advance- 

 ment of physics or of chemistry. The discovery of Graham as to the 

 characters of colloid substances and as to the diffusion of bodies in 

 solution through membranes would never have been made had not 

 Graham " plowed," so to speak, "with our heifer." The relations of 

 certain coloring matters to oxygen and carbon dioxide would have been 

 unknown had no experiments been made on the respiration of animals 



