THE GROWTH OF SCIENCE IN THE NINETEENTH CENTURY. 171 



of which the brain is made. We have learned by experiment and by 

 observation that the pattern of the web determines the plaj of the 

 impulses, and we can already explain many of the obscure problems 

 not only of nervous disease, but of nervous life, by an analysis which 

 is a tracking- out the devious and linked path of nervous threads. The 

 very beg-iiniing of this analysis was unknown in 1799. Men knew that 

 nerves were the agents of feeling and of the movements of muscles; 

 they had learned much about what this part or that part of the brain 

 could do; but the}^ did not know that one nerve liber differed from 

 another in the very essence of its work. It was just about the end of 

 the past century, or the beginning of the present one, that an English 

 surgeon began to ponder over a conception which, however, he did 

 not make known until some years later, and which did not gain com- 

 plete demonstration and full acceptance until still more 3'ears had 

 passed away. It was in 1811, in a tiny pamphlet published privately, 

 that Charles Bell put forth his New Idea that the nervous system was 

 constructed on the principle that "the nerves are not single nerves 

 possessing various powers, but l)undles of different nerves whose fila- 

 ments are united for the convenience of distribution, but which are 

 distinct in office as they are in origin from the brain." 



Our present knowledge of the nervous system is to a large extent 

 only an exemplification and expansion of Charles Bell's New Idea, and 

 has its origin in that. 



If we pass from the problems of the living organism viewed as a 

 machine to those presented by the varied features of the different 

 creatures who have lived or who still live on the earth, we at once call 

 to mind that the middle years of the present century mark an epoch 

 in biologic thought such as never came before, for it was then that 

 Charles Darwin gave to the world the Origin of Species. 



That work, however, with all the far-reaching effects which it has 

 had, could have had little or no effect, or, rather, could not have come 

 into existence, had not the earlier half of the century been in travail 

 preparing for its coming. For the germinal idea of Darwin appeals, 

 as to witnesses, to the results of two lines of biologic investigation 

 which were almost unknown to the men of the eighteenth century. 



To one of these lines 1 huve already referred. Darwin, as we know, 

 appealed to the geological record; and we also know how that record, 

 imperfect as it was then, and imperfect as it must always remain, has 

 since his time yielded the most striking proofs of at least one part 

 of his general conception. In 1799 there was, as we have seen, no 

 geological record at all. 



Of the other line I nuist say a few words. 



To-day the merest beginner in biologic study, or even that exemplai 

 of acquaintance without knowledge, the general reader, is aware that 

 every living being, even man himself, begins its independent existence 



