214 SECTIONAL ADDRESSES. 



available for effecting oxidations. Such was the service that this variation 

 rendered that it is safe to say that without it there could be no vertebrate 

 creation. It is this service that has made it possible for it to survive to 

 this day, when in the human species alone it is being produced at the 

 rate of about 10,000 tons a day. The story of the service of chlorophyll 

 would, of course, be more remarkable than this. 



Natural selection applies to the survival of the chemical forms of 

 living matter as it does to complex living organisms. These forms, 

 infinitely protean in their variety, survive and persist in so far and so 

 long as they minister to its self-regeneration. It is the principle of survival 

 by service. Function alone gives permanence to structure. Structure 

 without design is a pathological excrescence that has in itself the seeds 

 of its own destruction. What does not minister to self-regeneration has 

 no enduring share in life, for self-regeneration is the key to life. 



Why is it that what may be termed official physiology takes so little 

 cognisance of the doctrine of evolution ? These branches of biological 

 study appear to follow courses so exactly parallel that they never meet. 



The doctrine of evolution digs down into the foundations of scientific 

 philosophy. If a physiologist addressing physiologists ventures to say 

 anything on this subject of supreme appeal to all biologists it must be in 

 exaltation of the work of those who have approached it from the morpho- 

 logical side, and it may be in hopeful anticipation of the ultimate share 

 in the elucidation of some of its problems to be borne by physiology. 



On the part that function plays in the determination of structure it 

 is to be supposed that physiology will ultimately, at any rate, have some- 

 thing more to say. May I submit to the consideration of physiologists 

 certain points in the physiological development of the machinery of the 

 body where, unless I am mistaken, it is possible to detect the operation of 

 function in determining the design of the machine ? The properties and 

 behaviour of cells result from the properties and behaviour of the material 

 composing them. When a muscle-cell contracts this is, in general terms, 

 a reversible rearrangement of its parts in response to some alteration in 

 the distribution of forces within or about it due to a disturbance from 

 without. Such reversible reaction to adequate disturbance is a property 

 common in the material of which living cells are composed. In addition 

 to this reversible type of reaction there are irreversible reactions which 

 are characteristic of other kinds of cells, and it is what we call connective- 

 tissue cells that I would ask you to consider. There are several kinds of 

 connective-tissue cells, but they are alike in that they produce and dis- 

 charge into their vicinity material of a characteristic composition ; in 

 some of the commonest this material is chemically collagen, the substance 

 out of which gelatine can be obtained. In course of time these cells 

 come to be embedded in the material which they deposit about them- 

 selves and so form one kind of connective tissue. Cells capable of behaving 

 in this way are found, however, which have not yet exercised their faculty ; 

 these fibroblasts are then undifferentiated wandering cells that have found 

 no abiding-place in the community in which they have their birth. What 

 it is that makes them settle down and start producing the material in 

 which they come to be embedded has never yet been determined. But 

 the most striking structures to which they give rise are the tendons and 



