138 PROCEEDINGS OF SOCIETIES. 



into errors of interpretation conspicuous enough in the writings of 

 many of those who have preceded him. Again, in pathological micro- 

 scopical work, an immense field remains unexplored, waiting the 

 hand of the diligent to become rich in gems of priceless worth. 



But few students who commence the work of the microscope are 

 able to recognize the fact that, under high powers, the natural appear- 

 ance of almost every object is in some way influenced or altered by the 

 refractive nature of the fluid medium in which it has been immersed or 

 is examined. The remarkable changes effected by Graham's law of 

 diffusion when colloid substances enter into a preparation, at once 

 illustrates the necessity for caution in the use of preservative fluids. 

 The many changes brought about by glycerine in substances contain- 

 ing alkaline salts is another instance. 



There are, indeed, many other sources of error, to which, however, I 

 need not more particularly allude in addressing the members of this 

 Society, most of whom have already acquired skill in histological 

 science. Such work as I have endeavoured to sketch out, is necessarily 

 laborious and requires time and patience for its execution ; but he 

 who is prepared to undertake it will ultimately find his reward in 

 having extracted some secret from nature of inestimable worth. 



It is encouraging to think, and experience teaches us, that such 

 work can be done with instruments of an inexpensive kind. Neverthe- 

 less, I must candidly confess that I am unable to offer a model micro- 

 scope, well suited in every way for the work of the student in practical 

 histology. This has arisen from the circumstance that hitherto per- 

 sons, in no way fitted for the task, have volunteered to dictate the 

 form and accessories of students' microscopes. A society in no 

 especial manner engaged in the promotion of microscopical pursuits a 

 few years ago, ventured, I think, so far out of its way as to offer a pre- 

 mium for a " students' microscope" and not knowing anything about 

 the requirement of the class it was preparing to cater for, the whole 

 thing turned out a miserable failure. It would not have mattered 

 much if the mischief done could have been confined within the four 

 walls of the Society ; but this was impossible, and makers of micro- 

 scopes looked upon the Society of Arts' instrument as a model worthy 

 of imitation ; the result has been to drive teachers of practical 

 histology to use and prefer instruments of foreign workmanship. 

 The Medical Microscopical Society will, I feel sure, stimulate English 

 opticians to furnish a better and more efficient stand than either that 

 of Hartnack, Merz, or Nachet. We are favoured to-night with an 

 unusual display of students' microscopes, some of which are decidedly 

 in advance of the instrument usually met with. Mr. Baker contri- 

 butes a new microscope after Hartnack's model ; and Messrs. Beck, 

 Eoss, Browning, and Pillischer, well-known forms. But, in all, there 

 are faults of construction and room for improvement ; some are 

 wanting in firmness, the fine adjustment moves the object out of the 

 field of view, proving the instruments to be unsuited for the use of 

 high powers, and all lacking in one essential to a working microscope ; 

 a perfectly concentric turning stage, and without which it is almost 

 impossible to employ every kind of illumination or obtain high-power 



