NOVEMBEE 25, 1910] 



SCIENCE 



739 



ternal conditions and the effects that they 

 are observed to produce upon the organ- 

 ism. They give us no definite information 

 about the internal changes which, taken 

 together, constitute the response of the or- 

 ganism to external stimuli. As Darwin 

 wrote, there are two factors to be taken 

 into account — the nature of the conditions 

 and the nature of the organisms — and the 

 latter is much the more important of the 

 two. More important because the reac- 

 tions of animals and plants are manifold; 

 but, on the whole, the changes in the con- 

 ditions are few and small in amount. Mor- 

 phology has not succeeded in giving us any 

 positive knowledge of the nature of the 

 organism, and in this matter we must turn 

 for guidance to the physiologists, and ask 

 of them how far recent researches have re- 

 sulted in the discovery of factors compe- 

 tent to account for change of structure. 

 Perhaps the first step in this inquiry is to 

 ask whether there is any evidence of in- 

 ternal chemical changes analogous in their 

 operation to the external physical and 

 chemical changes which we have been deal- 

 ing with. 



There is a great deal of evidence, but it 

 is extremely difficult to bring it to a focus 

 and to show its relevancy to the particular 

 problems that perplex the zoologist. More- 

 over, the evidence is of so many different 

 kinds, and each kind is so technical and 

 complex, that it would be absurd to at- 

 tempt to deal with it at the end of an ad- 

 dress that has already been drawn out to 

 sufficient length. But perhaps I may be 

 allowed to allude to one or two generaliza- 

 tions which appear to me to be most sug- 

 gestive. 



We shall all agree that, at the bottom, 

 production and change of form is due to 

 increase or diminution of the activities of 

 groups of cells, and we are aware that in 

 the higher animals change of structure is 



not altogether a local affair, but carries 

 with it certain consequences in the nature 

 of correlated changes in other parts of the 

 body. If we are to make any progress in 

 the study of morphogeny, we ought to have 

 as exact ideas as possible as to what we 

 mean when we speak of the activities of 

 cells and of correlation. On these subjects 

 physiology supplies us with ideas much 

 more exact than those derived from mor- 

 phology. 



It is, perhaps, too sweeping a generaliza- 

 tion to assert that the life of any given 

 animal is the expression of the sum of the 

 activities of the enzymes contained in it, 

 but it seems well established that the ac- 

 tivities of cells are, if not wholly, at all 

 events largely, the result of the actions of 

 the various kinds of enzymes held in com- 

 bination by their living protoplasm. These 

 enzymes are highly susceptible to the influ- 

 ence of physical and chemical media, and 

 it is because of this susceptibility that the 

 organism responds to changes in the en- 

 vironment, as is clearly illustrated in a 

 particular case by Tower's experiments on 

 the production of color changes in potato- 

 beetles. Bayliss and Starling have shown 

 that in lower animals, protozoa and 

 sponges, in which no nervous system has 

 been developed, the response of the organ- 

 ism to the environment is effected by 

 purely chemical means. In protozoa, be- 

 cause of their small size, the question of 

 coadaptation of function hardly comes into 

 question; but in sponges, many of which 

 are of large size, the mechanism of co- 

 adaptation must also be almost exclusively 

 chemical. Thus we learn that the simplest 

 and, bj' inference, the phyletically oldest 

 mechanism of reaction and coordination is 

 a chemical mechanism. In higher animals 

 the necessity for rapid reaction to external 

 and internal stimuli has led to the develop- 

 ment of a central and peripheral nervous 



