OCTOBEE 24, 1913] 



SCIENCE 



583 



wreck, or need even have received any 

 damage, even on this occasion. The devils 

 are indeed represented in the tale as enti- 

 ties that from without entered into the 

 swine, as btdlets might have done. But the 

 running down into the sea is nur der 

 Ablauf der Lehenserscheinungen of the 

 swine themselves. Let bullets or bacteria, 

 poisons or compressed air, be the Beding- 

 ungen, the postulate that Virchow states will 

 remain irrefutable, if only it be interpreted 

 to meet the ease. For the principle merely 

 says that whatever entity it may be, fire or 

 air or bullet or poison or devil, that affects 

 the organism, the disease is not that entity, 

 but is the changed process of the organism. 

 What then is this hypothesis, this rejec- 

 tion of every external-entity-theory of dis- 

 ease, as the hypothesis appears when Vir- 

 chow writes these words in 1847 ? I reply, 

 this is no hypothesis in the stricter sense; 

 that is, it is no trial proposition to be sub- 

 mitted to precise empirical tests. It is, on 

 the contrary, a very precious leading idea. 

 It is equivalent to a resolution to search for 

 the concrete connection between the proc- 

 esses of any disease and the normal process 

 of the organism, so as to find the true unity 

 of the pathological and the normal process 

 through such a search. "Without some such 

 leading idea, the cellular pathology itself 

 could never have resulted ; because the facts 

 in question would never have been ob- 

 served. And I suppose that some equiva- 

 lent leading idea, if not precisely that which 

 Virchow stated in 1847, is just as precious 

 to you to-day in your own pathological 

 work. 



The value of such leading ideas for a 

 science lies in the sorts of research that 

 they lead men to undertake, and also in the 

 sorts of work that they discourage. They 

 are, I repeat, regulative principles. Obser- 

 vation does not, at least for the time, either 

 confirm or refute them. But, on the other 



hand, they awaken interest in vast ranges 

 of observation and experiment, and sus- 

 tain the patience and enthusiasm of work- 

 ers through long and baffling investigations. 

 They organize science, keep it in touch 

 with the spirit of the age, keep alive in it 

 the sense of the universal, and assure its 

 service to humanity. Specialism, without 

 leading ideas, remains but a sounding brass 

 and a tinkling cymbal. 



The sources of useful leading ideas seem 

 to me to be various. Social, and in partic- 

 ular industrial interests, suggest some of 

 them, as the perennial need of paying the 

 coal-bills for the steam engines suggested, 

 as we have seen, one of the leading ideas 

 which pointed the way towards the modern 

 theory of energy. The comparison of the 

 results of various sciences awakens such 

 leading ideas in various minds. Schleiden 

 set Schwamm searching for the basis of 

 the cell theory in animal tissues. That was 

 the suggestion of an hypothesis in the nar- 

 rower sense, to be tested. But when the 

 physical sciences set the students of organic 

 science to the work of conceiving organic 

 processes as mechanical in their inmost 

 nature, that was the suggestion of a leading 

 idea. 



But another source of such leading ideas 

 has been, upon occasion, philosophy. Phi- 

 losophy itself might be defined as a system- 

 atic scrutiny of leading ideas. It has also 

 proved to be often an inventor and inter- 

 preter of such ideas. Its faults in its work 

 have been frequent and obvious. In answer 

 to Dr. Councilman's request I have tried, 

 dispassionately, to point out such faults in 

 the Naturpfiilosophie. It has also been my 

 duty to point out some of the excellencies 

 that went with these defects. The moral of 

 my story is, I suppose, that it is the inter- 

 action of various types of human thought 

 and investigation, and not mutual isolation 

 or contempt, which helps us all, while he 



