702 



SCIENCE 



[N. S. Vol. XLII. No. 1090 



creative, after all, only in the ability to 

 make novel combinations of known ele- 

 ments. The successive steps in the prog- 

 ress of knowledge are absolutely essential. 

 The difference between the genius and the 

 common man is not that the former pro- 

 ceeds by longer steps, but that he takes 

 them more rapidly — often so rapidly that 

 he is hardly himself aware of the inter- 

 mediate positions. 



As an example of the results of the ex- 

 perimental method I want to speak first of 

 the progress of knowledge of the circu- 

 latory system — the heart and blood vessels 

 and their mode of functioning. 



The beginning of definite scientific 

 knowledge on this subject may be said to 

 date from the publication by "William 

 Harvey in 1628, of "De Motu Cordis et 

 Sanguinis," "The Movement of the Heart 

 and Blood." 



There was not lacking before the time of 

 Harvey quite complete and accurate knowl- 

 edge of anatomy of the organs of the cir- 

 culation ; the structure of the heart, the ar- 

 rangement and distribution of the blood 

 vessels, and the valves of the veins were 

 well known. Notwithstanding this there 

 existed in the minds of anatomists and med- 

 ical men the most bizarre and remarkable 

 explanations of the uses of these structures. 

 I can perhaps illustrate no better than by 

 a few quotations from Harvey showing the 

 kind of notions against which he had to 

 contend in teaching the doctrine of the 

 circulation of the blood. In the Introduc- 

 tion to "De Motu Cordis et Sanguinis": 



Did the arteries in tlieir diastole take air into 

 their cavities as commonly stated and in their sys- 

 tole emit fuliginous vapors by the same pores of 

 the flesh and skin; and further did they in the 

 time intermediate between the diastole and the 

 systole, contain air, and at all times either air, 

 or spirits or fuliginous vapors, what should then 

 be said to Galen, who wrote a book on purpose to 

 show that the arteries contained blood only? . . . 



And if the arteries in their systole expel 



fuliginous vapors from their cavities through the 

 pores of the flesh and skin, why not the spirits, 

 which are said to be contained in these vessels, at 

 the same time, since spirits are much more subtle 

 than fuliginous vapors, or smoke? 



But Harvey, instead of merely specu- 

 lating upon the functions as they might be 

 inferred from appearances in the dead 

 animal, put everything possible to the test 

 of observation and experiment in the living 

 animal, and as a result was able to state his 

 reasons for the belief in the circulation of 

 the blood in language which can hardly be 

 improved upon to-day. The different atti- 

 tude of mind resulting from his practise of 

 observation and experiment is shown in 

 his assertion 



That the facts cognizable by the senses wait 

 upon no opinions, and that the works of nature 

 bow to no antiquity; for indeed there is nothing 

 more ancient or of higher authority than nature. 



Contrast with this the views against 

 which he had to strive as shown by another 

 quotation from the same book: 



Medical schools admit three kinds of spirits; the 

 natural spirits flowing through the veins, the vital 

 spirits through the arteries, and the animal spir- 

 its through the nerves. . . . 



Farther, besides the three orders of influxive 

 spirits adverted to, a like number of inplanted or 

 stationary spirits seem to be acknowledged; but 

 we have found none of these spirits by dissection, 

 neither in the veins, nerves, arteries, nor other 

 parts of living animals. 



It was never permitted Harvey to know 

 the exact method by which the blood passed 

 from the terminations of the arteries to the 

 beginnings of the veins; for no microscope 

 suitable for the observation of the capil- 

 laries had then been invented. This final 

 step was reached by Malpighi in 1661 just 

 four years after Harvey's death. 



After the fact of the circulation had been 

 established, it began to be possible to inves- 

 tigate the mode of working of the circu- 

 latory apparatus. The first important step 

 in this direction was taken by the Reverend 



