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POPULAR SCIENTIFIC LECTURES. 



mpdicino. 



\Vo may admit Ibis if only \ve once agree 

 what wo nre to understand as a philosopher. 

 Fur thrt ancients, philosophy embraced all 

 theoretical knowledge ; their philosophers 

 pursued mathematics, physics, astronomy, 

 uatur.il history, in close connection with true 

 philosophical or metaphysical considerations. 

 li', therefore, we are to understand the med- 

 ical philosopher of Hippocrates to be a man 

 who has a perfected insight into the causal 

 connection of natural processes, we shall in 

 fact bo able to say with Hippocrates, Such a 

 one can give help like a god. 



Understood in this sense, the aphorism 

 describes in three words the ideal which our 

 science has to strive after. But who can 

 allege that it will ever attain this ideal ? 



But those disciples of medicine who 

 thought themselves divine even in their own 

 lifetime, and who wished to impose them- 

 selves upon others as such, were not inclined 

 to postpone their hopes for so long a period. 

 The requirements for the QiAuanijto; were con- 

 siderably moderated. Every adherent of any 

 given cosmological system, in which, for well 

 or ill, facts must be made to correspond with 

 reality, felt himself to be a philosopher. 

 The philosophers of that time knew little 

 more of the laws of nature than the unlearned 

 layman ; but the stress of their endeavors 

 was laid upon thinking, upon the logical con- 

 sequence and completeness of the system. 

 It is not difficult to understand how in peri- 

 ods of youthf ul development, such a one-sided 

 overestimate of thought could be arrived at. 

 The superiority of man over animals, of the 

 scholar over the barbarian, depends upon 

 thinking ; sensation, feeling, perception, on 

 the contrary, he shares with his lower fellow- 

 creatures, and in acuteness of the senses 

 many of these are even superior to him. 

 That man strives to develop his thinking 

 faculty to the utmost is a problem on the 

 solution of which the feeling of his own dig- 

 nity, as well as of his own practical power, 

 depends ; and it is n natural error to have 

 considered unimportant the dowry of mental 

 capacities which nature had given to animals, 

 and to have believed that thought could bo 

 liberated from its natural basis, observation, 

 and perception, to begin its Icarian flight of 

 metaphysical speculation. 



It is, in fact, no easy problem to ascertain 

 completely the origins of our knowledge. An 

 enormous amount is transmitted by speech 

 and writing. This power which man pos- 

 sesses of gathering together the stores of 

 knowledge of generations, is the chief reason 

 of his superiority over the animal, who is re- 

 stricted to an inherited blind instinct and to 

 its individual experience. But all transmit . 

 ted knowledge is handed on already formed ; 

 whence the reporter has derived it, or how 

 much criticism he has bestowed upon it, can 

 seldom bo made out, especially if the tra- 

 lition has been handed down through sev- 

 eral generations. We must admit it all upon 

 good faith ; we cannot arrive at the source ; 

 and when many generations have contented 





themselves with such knowledge, havo 

 bi ought no criticism to bear upon it ; have, 

 iadi-ed, gradually added all kinds of small 

 alterations, which ultimately grew up to 

 large ones after all this, strange things aro 

 often reported and believed under the 

 authority of primeval wisdom. A curious 

 case of this kind is the history of the circula- 

 tion of the blood, of which we shall still have 

 to speak. 



But another kind of tradition by speech, 

 which long remained undetected, is even 

 still more confusing for one who reflects upon 

 the origin of knowledge. Speech cannot 

 readily develop names for classes of objects 

 or for classes of processes, if we have not 

 been accustomed very often to mention 

 together the corresponding individuals, 

 things, and separate cases, and to assert 

 what there is in common about them. They 

 must, therefore, possess many points in com- 

 mon. Or if we, reflecting scientifically upon 

 this, select some of these characteristics, and 

 collate them to fcrm a definition, the com- 

 mon possession of these selected characteris- 

 tics must necessitate that in the given cases a 

 great number of other characteristics are to 

 be regularly met with ; there must be a nat- 

 ural connection between the first and tba 

 last-named characteristics. If, for instance, 

 we assign the name of mammals to those ani- 

 mals which, when young, are suckled by 

 their mothers, we can assert further, in 

 reference to them, that they aro all warm- 

 blooded animals, born alive, that they have a 

 spinal column but no quadrate bone, breathe 

 through lungs, have separate divisions of the 

 heart, etc. Hence the fact, that in the 

 speech of an intelligent observing people a 

 certain class of things are included in one 

 name, indicates that these things or cases fall 

 under a common natural relationship ; by 

 this alone a host of experiences are transmit- 

 ted from preceding generations without this 

 appearing to be the case. 

 "The adult, moreover, when he begins to re- 

 flect upon the origin of his knowledge, is in 

 possession of a huge mass of every-day ex- 

 periences, which in great part reach back to 

 the obscurity of his first childhood. Every- 

 thing individual has long been forgotten, but 

 the similar traces which the daily repetition 

 of similar cases has left in his memory haw 

 deeply engraved themselves. And since only 

 that which is in conformity with law is 

 always repeated with regularity, these deeply 

 impressed remains of all previous concep- 

 tions are just the conceptions of what is con- 

 formable to law in the things and processes. 



Thus man, when he begins to reflect, finds 

 that he possesses a wide range of acquire- 

 ments of which he knows not whence they 

 came, which he has possessed as long ns ho 

 can remember. We need not refer even to 

 the possibility of inheritance by procreation. 



The conceptions which he has formed, 

 which his mother tongue has transmitted, 

 assert themselves ns regulative powers, even 

 in the objective world of fact, and as he does 

 not know that he or his forefathers havo de- 



