viii AUTHOR'S PREFACE. 



when such a rapid accumulation of facts is taking place, as there is 

 in ours, we are doubly bound to render our knowledge accessible to 

 the whole body of our professional brethren. We would have 

 reform, and not revolution : we would preserve the old, and add the 

 new. But our contemporaries have a confused idea of the results 

 of our activity. For only too much it is apt to appear as though 

 nought but a confused and motley mass of old and new would 

 thereby be obtained ; and the necessity of combatting rather the 

 false or exclusive doctrines of the more modern, than those of the 

 older writers, produces the impression that our endeavours savour 

 more of revolution than reformation. It is, no doubt, much more 

 agreeable to confine oneself to the investigation and simple publica- 

 tion of what one discovers, and to leave to others to " take it to 

 market" (verwerthen exploiter), but experience teaches us that 

 this is extremely dangerous, and in the end only turns out to the 

 advantage of those who have the least tenderness of conscience. 

 Let us undertake, therefore, every one of us to fulfil the duties both 

 of an observer and of an instructor. 



The lectures, which I here publish with the view of accomplishing 

 this double purpose, have found such very patient auditors, that 

 they may perhaps venture to hope for indulgent readers likewise. 

 How greatly they stand in need of indulgence, I myself feel very 

 strongly. Every kind of lecture can only satisfy the actual hearers ; 

 and especially when it is chiefly intended to serve as an explanation 

 of drawings on a board, and microscopical preparations, it must 

 necessarily appear heterogeneous and defective to the reader. When 

 the intention is to give a concise view of a comprehensive subject, 

 it necessarily becomes impossible to bring forward all the arguments 

 that could be advanced, and to support them by the requisite quo- 

 tations. In lectures such as these too the personal views of the lec- 

 turer may seem to be brought forward with undue exclusiveness, but 

 as it is his business to give a clear exposition of the actual state of 

 the science of which he treats, he is obliged to define with precision 

 the principles, the correctness of which he has proved by his own 

 experience. 



I trust therefore that what I offer may not be taken for more than 

 it is intended to be. Those, who have found leisure enough to keep 



