POPULAR SCIENTIFIC LECTURES. 



veloport these conceptions from the tilings 

 themselves, the world of facts seems to him, 

 like his conceptions, to bo governed by in- 

 tdlcctual forces. Wo recognize this psycho- 

 logical anthropomorphism, from the Ideas of 

 Plato, to the immanent dialectic of the cos- 

 micul process of Hegel, and to the uncon- 

 scious will of Schopenhauer 



Natural science, which informer times was 

 virtually identical with medicine, followed 

 the path of philosophy : the. deductive 

 method seemed to be capable of doing every- 

 thing. Socrates, it is true, had developed 

 the inductive conception in the most instruc- 

 tive manner. But the best which he accom- 

 plished remained virtually misnr^r- ".><:. 



I will not lead you through the motley con- 

 fusion of pathological theories which, accord- 

 ing to the varying inclination of their 

 authors, sprouted up in consequence of this 

 or the other increase of natural knowledge, 

 and were mostly put forth by physicians, who 

 obtained fame and renown as great observers 

 and empirics, independently of their theories. 

 Then canio the less gifted pupils, who copied 

 their master, exaggerated his theory, made it 

 more one-sided and more logical, without re- 

 gard to any discordance with nature. The 

 more rigid tho system, the fewer and the, 

 more thorough were the methods to which 

 the healing art was restricted. The more tho 

 schools were driven into a comer by the in- 

 crease in actual knowledge, the more did they 

 depend upon the ancient authorities, and tho 

 more intolerant were they against innova- 

 tion. The great reformer of anatomy, Vesa- 

 lius, was cited before the theological faculty 

 of Salamanca ; Servetua was burned at 

 Geneva along with his book, in which ho do- 

 scribed the circulation of the lungs ; and tho 

 Paris faculty prohibited the teaching of Har- 

 vey's doctrine of the circulation of the blood 

 in its lecture-rooms. 



At tho same time the bases of tho systems 

 from which these schools started were mostly 

 views on. natural science which it would have 

 Iwen quite right to utilize within a narrow 

 circle. What was not right was tho delusion 

 that it was more scientific to refer ail diseases 

 to one kind of explanation, than to several. 

 What was called the solidar pathology want- 

 ed to deduce even-thing from the altered 

 mechanism of tho solid parts, especially from 

 their altered tension ; from the stridwn and 

 iaxum. from tone and want of tone, and after- 

 ward from strained or relaxed nerves and 

 from obstructions in tho vessels. Humoral 

 pathology was only acquainted with altera- 

 tions in mixture. The four cardinal fluids, 

 representatives of tho classical four elements, 

 blood, phlegm, black and yellow gall ; with 

 others, the acrimonies or dyscrasies, which 

 had to be expelled by sweating and purging ; 

 in the beginning of our modern epoch, the 

 acids and alkalies or the alchemistic spirits, 

 und the occult qualities of the substances 

 assimilated -all these were the elements of 

 this chemistry. Along with these were found 

 all kinds of physiological conceptions, some 

 of which contained remarkable- forcshadow- 



ings, such AS the f/t^vrnv Vtp/iov, the inherent 

 vital force of Hippocrates, which is kept up 

 by nutritive substances, this again boils i:\ 

 the stomach and is the source of all motion ; 

 here the thread is begun to be spun which 

 subsequently led a physician to the law of 

 the conservation of force. On the othff 

 hand, the jrrriyta which is half spirit and 

 half air, which can be driven from the lungs 

 into the arteries and fills them, has produced 

 much contusion. The? fact that air is generally 

 found in the arteries of dead bodies, which 

 indeed only penetrates in tho moment- iu 

 which the vessels are cut, led the ancients to 

 the belief that air is also present in the arte- 

 ries during life. The A r eins only remainosl 

 then in which blood could circulate. It was 

 believed to be formed in the liver, to mov.-i 

 from there to the heart, and through tho 

 veins to the organs. Any careful observation 

 of the operation of blood-letting must hav 

 taught that, in the veins, it comes from tbo 

 periphery, and flows toward tho heart. But 

 this false theory had become so mixed up with 

 the explanation of fever and of inflammation, 

 that it acquired the authority of a dogma, 

 which it v/as dangerous to attack. 



Yet tho essential and fundamental error c 

 this system was, and still continued to be, 

 the false kind of logical conclusion to which 

 it wa.s supposed to lead : the conception 

 that it must be possible to build a complete 

 system which would embrace all forms of 

 disease, and their cure, upon any one such 

 simple explanation. Complete knowledge of 

 the causal connection of one class of phe- 

 nomena gives finally a logical coherent sys- 

 tem. There i.s no prouder edifice of tho most 

 exact thought than modern astronomy, de- 

 duced even to the minutest of its small dis- 

 turbances, from Newton's law of gravitation. 

 But Newton had been preceded by Kepler, 

 who had by induction collated all the facts ; 

 and the astronomers have never believed that 

 Newton's force excluded the simultaneous! 

 action of other forces. They have been con- 

 tinually on the watch to see whether friction, 

 resisting media, r.nd swarms of meteors have 

 not also some influence. The older philoso- 

 phers and physicians believed they couM 

 deduce, before they had settled their general 

 principles by induction. They forgot that u 

 deduction can have no more certainty than 

 the principle from which it is deduced ; and 

 that each new induction must in tho first 

 place bo a new test, by experience, of its own 

 bases. That, a conclusion is deduced by tho 

 strictest logical method from an uncertain 

 premiss does not give it a hair's breadth of 

 certainty or of value. 



One chamet eristic of tho schools which 

 built up their system on such hypotheses, 

 which they assumed as dogmas, is the in- 

 tolerance of expression which I have already 

 partially mentioned. One who works upon 

 a well-ascertained foundation may readily ad- 

 mit an error ; he loses, by so doing, nothing 

 more than that in which ho erred. If, how- 

 ever, the starting-point has boen placed upon 

 a hypothesis, which either appears guaranteed 



