1864.] 



President's Address, 



5m 



reward for his enlightened and persevering labour in investigating the 

 structure of the central organs of the nervous system, we may not 

 inappropriately recal to mind that one of those who, in former times, 

 most signally advanced this department of anatomical knowledge was 

 an early Fellow of this Society, Dr. Thomas Willis, and that his cele- 

 brated treatise on the Anatomy of the Brain was illustrated by draw-, 

 ings from the pencil of no less eminent an associate than Sir 

 Christopher Wren, also a Fellow, and afterwards President of the 

 Society. But in that day, and down to a recent period, the investiga- 

 tion was carried on with the naked eye, and accordingly the more 

 intimate structure and organization were hidden from view until 

 brought to light in our own time by the aid of the microscope. It is 

 true that the tissue of the brain and nerves did not escape the notice 

 of the earlier microscopic observers ; of this, indeed, there is well- 

 known evidence in the early volumes of our own Transactions; still 

 their inquiries were almost entirely confined to the microscopic cha- 

 racters of the fibres and other constructive elements of the cerebral and 

 nervous tissues, whereas the application of the microscope, in tracing 

 the arrangement of these elements, and their combination into an 

 organized structure, dates little further back than the last twenty years. 



In this field of inquiry Mr. Clarke has been one of the most able 

 and successful workers. No sooner had he entered upon it than he 

 introduced an important improvement into the method of investiga- 

 tion. The observations had previously been made on opaque sections 

 of the parts examined, on which only the coarser features of the struc- 

 ture could be discerned ; but Mr. Clarke devised a process for render- 

 ing them transparent, whereby it became possible to trace the finer 

 and more intimate arrangement ; and this method has not only, in his 

 own hands, proved fruitful in valuable results, but, having been adopted 

 by his fellow-labourers in the same pursuit, has been most influential 

 on the general progress of the inquiry. 



The investigation itself, even with every available aid, is singularly 

 difficult and laborious. Section after section of the spinal cord through- 

 out its whole length, and of its complex cranial prolongation, must be 

 carefully scrutinized, thoughtfully compared, and, for the most part, 

 minutely delineated ; and sometimes many diff'erent specimens must 

 be prepared and examined in order to make out a single point. In 

 this exhausting work Mr. Clarke has long and meritoriously persevered 

 amid the calls of an active professional life. The results of his 

 labours are made known in his various papers, published chiefly 

 in the Philosophical Transactions, and in the elaborate delineations 

 with which they are illustrated. And it is pleasing to know that, in 

 all essential points, his observations have been confirmed by the most 

 accurate and trustworthy of his contemporaries. 



After what has been said of the difficulties of the inquiry, it will be 



