INTRODUCTORY REMARKS. 23 



allow a fluid to pass but one way. All the philosophical 

 reasoning, however, of this celebrated man could not 

 establish, what appears to us so plain a truth, until it was 

 evidenced in the circulation of cold-blooded animals by 

 means of the microscope, and thus placed beyond a 

 doubt. Discerning, as we can do, the very forms of the 

 globules of that fluid, as they flow through the capillaries 

 from the arteries to the veins, in obedience to the laws 

 impressed upon them by the Almighty Creator — viewing 

 this most sublime phenomenon, by which life itself is 

 diffused throughout, and sustained in every part of the 

 system — who can resist conviction of the great truth ? 



Nor is it a matter of less importance in a scientific 

 point of view, or less interesting, that by the same 

 means we can perceive the fibrous structure of the 

 muscles and nerves, the form and arrangement of the 

 canals by which the internal cavities of the bones are 

 lubricated and nourished, the glandular structure of that 

 beautiful and complex apparatus by which the secretions* 1 

 are carried on — all, and each of these, requiring but the 

 aid of one of our improved microscopes to render them 

 distinctly visible. Again : how admirably developed by 

 means of the microscope are the curious and complex 

 structures of the eyes of insects, the crystalline lenses of 

 those of fish, birds, &c.f and many of the other parts of 

 the visual organs];. The eye — that useful and delightful 



* Nouvelles Rccherches sur la Structure de la Peau, par M. Breschet. 

 I Philosophical Transactions, 1833. 

 I Sec Langentoeck ou the Lye. 



