DR. HOllATlO WOOD ON FRESH WATER ALGM. 195 



bottle half-full of water, and sluike the whole violently, drawing off 

 the water from the plants in some way, and repeating the process 

 with fresh additions of water, until the plants are well scoured. 

 At first sight, this process would seem exceedingly rough, and 

 liable to spoil the specimens, but I have never seen bad results 

 from it, at least when practised with judgment. The water seems 

 so to envelope and protect the little plants, that they are not 

 injured. 



After all, in many instances it appears impossible to clean these 

 Algae without utterly ruining and destroying them, so that he who 

 despises and rejects mounted specimens simply because they are 

 dirty and unsightly, will often reject that which, scientifically speak- 

 ing, is most valuable and attractive. 



In finally mounting these plants, the only proper way is to place 

 them in some preservative solution within a cell on a slide. After 

 trial of solution of acetate of alumina and various other preser- 

 vative fluids, I have settled upon a very weak solution of carbolic 

 acid, as the best possible liquid to mount these plants in. Acetate 

 of alumina would be very satisfactory were it not for the very great 

 tendency of the solution to deposit minute granules, and thus spoil 

 the specimens. As every one knows, the great difficulty in pre- 

 serving microscopic objects in the moist way is the perverse ten- 

 dency of the cells to leak, and consequently slowly to allow entrance 

 to the air and spoil the specimens. 



As I have frequently found to my great chagrin, the fact that 

 a slide has remained unchanged for six months, or even a year, is 

 no guarantee that i^ will remain so indefinitely. It becomes, 

 therefore, exceedingly important to find some way of putting up 

 microscopic objects that can be relied on for their preservation. 

 Where carbolated glycerine jelly or Canada balsam can be used, 

 the solid coating which they form around tlie specimens constitutes 

 the best known protection. Except in case of the Diatoms, how- 

 ever, these substances so shrivel and distort the fresh water algas 

 immersed in them as to utterly ruin them. I lost so many 

 specimens by the old ways of mounting, that, becoming dis- 

 heartened, I gave up all idea of making a permanent cabinet, 

 until a new cement, invented by Dr. J. G. Hunt, of this city, was 

 brought to my notice. This is prepared as follows : — 



Take damar gum, any quantity, and dissolve it in benzole ; the 

 solution ma^ be hastened by heat. After obtaining a solution just 



