334 LII'E : OUTLINES OF GENERAL BIOLOGY 



certain conditions, realised in the living cell, it reacts with the 

 oxygen extenially supplied, and is able to pass it on indirectly to the 

 food-materials in the tissues. It was a great step when Lavoisier put 

 the living organism beside the lighted candle and elucidated the 

 combustion or oxidation going on in both; but there has always been 

 the lurking difficulty that the numerous and very rapid energy- 

 yielding reactions in the tissues take place at a low tempera- 

 ture. This is now explained by the discovery of the "oxygen-trans- 

 porting" function of glutathione, which is widely distributed in 

 plants and animals. Here one might continue the subject by 

 referring to Keilin's discovery of a widely distributed cell-pigment, 

 cytochrome, which has to do with the control of oxygen within 

 the cell. 



As a second modern example of the assistance that chemistry is 

 always giving to biology, we may take the contraction of muscle, 

 the subject of more investigations than any other function. The 

 problem of the contraction of a muscle fibre is still but partially 

 solved, but our point at present is simply this, that its aspect was 

 entirely changed by the chemical researches of Fletcher and Hopkins. 

 These researches showed that the stimulation of the muscle fibre is 

 associated with the liberation of lactic acid, which in some way or 

 other induces a physical change in the muscle fibrils, namely, 

 contraction. It may be, as we have seen, that the liberated lactic 

 acid raises the surface-tension at the surfaces at which it is produced, 

 so that they tend, for instance, to become more spherical, or it may 

 be that the production of lactic acid withm a semi-permeable 

 membrane attracts water and induces swelling. This does not concern 

 us just now: the point is that a chemical change, in which there is 

 production of lactic (and perhaps phosphoric) acid, induces a 

 physical change ; and that the production of lactic acid is essential. 

 Thus we can understand better why there must be a reinstatement 

 of the lactic acid or its chemical precursor into the fibre if it is to 

 continue effective; and there are interesting theories which suggest 

 how this restitution of lactic acid may be effected. But the point is 

 that, even with the everyday function of contractility, progress in 

 understanding is largely dependent on chemistry and physics. 



Now, we might continue with other functions of the body, and 

 show how chemistry helps the biologist to understand them; but our 

 study cannot be more than illustrative. Moreover, it must be noted 

 that in many cases, like the circulation of the blood, physics has 

 more to say than chemistry. As to endocrinal influences and reflex 

 actions, neither chemistry nor physics has as yet any illuminating 

 suggestion to offer. So we change our outlook. 



Sometimes it seems fair to say that the help chemistry gives 

 biology is not so much an idea as an opportunity. When Lavoisier 

 said "living is burning", that was a clarifying idea; but it is other- 



