vi 



is presented. From tin- experience gained liy teach- 

 ing during more than fifteen years, 1 believe that I 

 have ;ic(juircd sufficient clearness of ( xpre -ion, even in 

 treating of more difficult matters, to be intelligible 

 when studied carefully even by tlu.se who are not 

 specialists. In crrtain cases it lias been impossible to 

 avoid somewhat long explanations of physical and. 

 especially, of electric phenomena. But these have 

 been confined to the narrowest possible limits, and I 

 must refer those who require further details to my 

 Elektridtdtslehre //'// .lAr-//,'//^/- (lierlin, Ilirschwald). 

 It has also been unavoidable in giving an account of 

 one branch of Physiology to indicate the connection 

 with other branches, though it has been impossible to 

 enter into the details of these. To those who feel 

 inclined to follow these matters further, I recommend 

 the study of Huxley's ' Elementary Physiology.' Cer- 

 tain details, which would have detained the course of 

 the text too long, I have relegated to the Notes and 

 Additions at the end of the book. 



In accordance with the title of the book, I have 

 omitted too scientific proofs, references, &<. The 

 names of men of science to whom the discovery of the 

 facts is due have only been occasionally introduced. 

 In this matter no fixed rule has been followed, but it 

 did not seem riidit to omit occasional mention of the 

 names of the chief founders of this branch of know- 

 ledge I'd. Weber, K. du Bois-Reymond, and II. Ilelm- 

 holtz. 



Kia.\Noi:\ : April 15, 1677. 



