40 INTRODUCTION. 



With respect to the first point, the fluid which I have found 

 to answer best is made in the following way : — To sixteen 

 parts of distilled ivater add one part of rectified spirits of wine 

 and a few drops of creosote sufficient to saturate it ; stir in a 

 small quantity of prepared chalk and then filter : with this 

 fluid mix an equal measure of camphor -water (water satu- 

 rated with camphor), and before using strain off through a 

 piece of fine linen. 



" This fluid I do not find to alter the appearance of the 

 endochrome of Algse more than distilled water alone does 

 after some time, and there is certainly less probability of con- 

 fervoid filaments making their appearance in the prepa- 

 rations ; and there would seem to be nothing to prevent 

 such a growth from taking place when the object is mounted 

 in water only, provided a germ of one of these minute plants 

 happen to be present, as well as a small quantity of free 

 carbonic acid. 



"Fluids containing a larger quantity of spirits of wine, 

 and consequently of creosote also, than the one of which I 

 have given the formula, produce a greater change in the 

 appearance of the endochrome. I at one time thought that by 

 increasing the density of the mounting fluid, the endochrome 

 of the plant might be less disturbed, and I dissolved a small 

 quantity of sugar in the fluid ; but this made the cell-mem- 

 brane too transparent, and rendered completely invisible the 

 gelatinous sheath with which many species of Algae are 

 furnished. 



" I now proceed to describe my method of making cells 

 in which to mount preparations of Algse. Some objects re- 

 quire very shallow and others somewhat deeper cells. The 

 former may be made with a mixture of japanners' gold-size 

 and litharge, to which (if a dark colour is preferred) a small 

 quantity of lamp-black can be added. These materials 

 should be rubbed up together with a painter's muller, and 

 the mixture laid on the slips of glass with a camel-hair 

 pencil as expeditiously as possible, since it quickly becomes 

 hard ; so that it is expedient to make but a small quantity at 



