10 THE AMERICAN MONTHLY [Jan 



that if the diatoms were cleaned with acid and were not 

 properly washed afterwards some of the mounting- media 

 would be affected in the way suggested, the perfection of 

 the structure in his slide was no doubt due to the fact that 

 the material had not been previously over-cooked. 



The President thought that in considering the special 

 forms which silica might take in the structure of a diatom 

 a possible explanation might be found on the theory that 

 the process of deposit might be a vital process and not a 

 mechanical one. 



Mr. Ingpen said he was much inclined to this view, and 

 often thought that the development of a diatom might be 

 somewhat the same as the formation of a shell, where the 

 animal absorbed lime in a soluble form on one side and de- 

 posited it in an insoluble form on the other side. The ter- 

 tiary structure might possibly be the very origin of the 

 diatom. 



On Some Micro-Cements for Fluid Cells. 



BY CHARLES F. ROUSSLETT. 

 BEAD BEFORE THE QUEKETT CLUB. 



Three years ago I read a note on Clarke's Spirit-proof 

 Micro-Cements, which had proved reliable for many years 

 in securely sealing micro cells containing methylated 

 spirit. I then recommended this same cement for cells 

 containing watery fluids. It appears, however, that I too 

 hastily jumped to the conclusion that, because this 

 cement is good for spirit mounts, h would also be equally 

 good for watery fluids, a conclusion which seems natural 

 enough. After three years' experience I must pronounce 

 it a complete failure as regards watery fluid mounts, 

 while the spirit mounts remain as good as before; and 

 I hasten to communicate these facts, so that others may 

 profit by my experience. 



The possession of .a thoroughly good and reliable 

 cement for fluid, and especially watery fluid mounts, is so 

 important to microscopists, that I hope all who have any 



