PREPARATION OF OBJECTS FOR THE MICROSCOPE. 153 



of any kind, that is not a thorough and complete solution in all 

 its parts. This is the experience of all microscopists. Dr. Car- 

 penter, who as you know is no mean authority, says : " The 

 varnishes used for mounting objects in liquid should always be 

 such as contain no mixture of solid particles. This is a principle 

 on which the author from an experience of many years is 

 disposed to lay great stress." He says, "that he has always 

 found that such cements (mechanical mixtures), although they 

 may stand well for a few weeks or months, become porous after 

 a greater lapse of time, allowing the evaporation of the liquid 

 and the admission of air." White zinc cement may answer for 

 finishing purposes, if used with great caution ; but it is at best 

 a very treacherous material, insidiously working its way into 

 places where it has no business to be. It has caused more failures 

 than any other material we work with. I know that nine-tenths 

 of my lame ducks have white feet. 



In conclusion I would remark that there is a strange fascina- 

 tion in the art of the microscopist. It has been the life work of 

 many men of cultivated and superior minds. It has been the 

 recreation of a vast number of scientific and professional men. 

 Those who have once taken it up in the love of it, have seldom 

 laid it aside. There is in it the widest field for the display of 

 ingenuity and artistic taste, together with the fullest scope for 

 research and new discoveries. To the gratification of accom- 

 plishing a new process or of finding a new object of interest or 

 beauty, there is added the highest incentive which is now left to 

 the man of science that of searching out the secrets of nature 

 on the border-land of the invisible. Be assured that the field of 

 labor and research to which this evening I seek to incite your 

 exertion and your emulation, is at once the most fascinating, the 

 most important, and the most honorable of the occupations of 

 cultured minds. 



