vi PREFACE TO THE AMERICAN EDITION. 



A short account of American Microscopes, their modifications 

 and accessories, has also been added, and the whole Appendix 

 has been fully illustrated, through the liberality of the Pub- 

 lishers, by the addition of upwards of one hundred wood- 

 engravings. 



FRANCIS GURNEY SMITH, M.D. 



428 WALNUT STREET, 

 June, 1856. 



