18 THE MICROSCOPIST. 



the observations of those who boil, roast, macerate, putrefy, 

 triturate, and otherwise injure the delicate tissues ? Most of 

 the tissues contain albumen, which, so treated, gives origin to 

 globules, and flakes of different forms ; a circumstance which 

 has led several anatomists to conceive the basis of animal 

 structures to be globular. Several late observers have also 

 made this mistake. 



Messrs. Todd and Bowman, the learned authors of " The 

 Physiological Anatomy and Physiology of Man," present the 

 following sensible remarks respecting this subject, " To make 

 microscopical observation really beneficial to physiological 

 science, it should be done by those who possess two requisites : 

 an eye, which practice has rendered familiar with genuine 

 appearances as contrasted with those produced by the various 

 aberrations to which the rays of light are liable in their passage 

 through highly refracting media, and which can quickly 

 distinguish the fallacious from the real form; and a mindj 

 capable of detecting sources of fallacy, and of understanding 

 the changes which manipulation, chemical reagents, and other 

 disturbing causes may produce in the arrangement of the ele- 

 mentary parts of various textures. To these we will add 

 another requisite, not more important for microscopical than 

 for other inquiries ; namely, a freedom from preconceived 

 views or notions of particular forms of structure, and an ab- 

 sence of bias in favor of certain theories, or strained analogies. 

 The history of science affords but too many instances of the 

 baneful influence of the idola spectis upon the ablest minds ; 

 and it seems reasonable to expect that such creatures of the 

 fancy would be especially prone to pervert both the bodily and 

 the mental vision, in a kind of observation which is subject to 

 so many causes of error, as that conducted by the aid of the 

 microscope." 



The invention of the achromatic object-glasses for micro- 



