ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 159 



until all trace of chromic acid is got rid of. A mixture of alcohol 

 and glycerin is then added to the water, and the proportion of these 

 latter is gradually increased until the Medusae come to be in a pure 

 solution of glycerin and alcohol, which is made of the same specific 

 gravity as sea-water. 



Mounting' Diatoms in situ.* — Dr. F, L. James has found that the 

 processes commonly in use, and recommended in the text-books for 

 preserving diatoms, as well as other minute aquatic organisms, desmids, 

 algse, &c., in the natural state, are all of them more or less unsatis- 

 factory, and he never succeeded in making a really good mount until 

 he came across a letter from Mr. C. H. Stodder, of Boston,| giving 

 his method of mounting in situ, which is briefly as follows : — 



" The algfe upon which the diatoms are growing are thoroughly 

 dried, as usual, on bibulous paper. It is presupposed that all extra- 

 neous dirt, &c., has been removed. I have provided a slide with a 

 circle of ink marking the centre on the reverse side, clean cover-glass, 

 a bottle of chloroform solution of Canada balsam, some chloroform, 

 and a watch-glass. These must all be ready at hand, as the operation 

 must be carried through quickly. I select a bit of the weed, just 

 large enough to mount, put a few drops of chloroform in the glass, 

 and immerse the weed in it. The chloroform seems to be as efficient 

 as water in restoring the dried alga to its natural shape. As it 

 evaporates quickly, a few drops should be added from time to time 

 until the alga is thoroughly permeated and has a natural appearance. 

 It is then transferred to the slide, covered with a drop or two of 

 chloroform, and arranged in the position which it is to occupy. A 

 drop of balsam is now put on, before the chloroform has .entirely 

 evaporated, and the cover-glass applied. When thus manipulated, 

 the balsam follows the chloroform, penetrates the cells of the weed, 

 and makes them translucent so as to show all the details of their 

 structure admirably, and the diatoms are displayed adhering in their 

 natural positions. The balsam must be allowed to harden slowly, as 

 it will not do to apply heat, since there is danger of shrivelling the 

 delicate structures by so doing. 



While the specific markings of diatoms can rarely be shown in 

 mountings of this description, what is equally important, the mode 

 of growth, can thus be demonstrated — which cannot be with cleaned 

 diatoms. I have before me a slide of Ptilota, from the Pacific, which 

 displays finely several species of diatoms of which I had seen no trace 

 .until this method was tried. If you have a number of specimens to 

 mount at once, it will be better to put them directly into a small 

 bottle of chloroform instead of the watch-glass. They can thence be 

 taken directly to the slide, well saturated with chloroform. The 

 most important point is to add the balsam before the chloroform has 

 evaporated." 



The method of Mr. Stodder gives equally good results with fresh- 

 er salt-water algas. 



* St. Louis National Druggist, vii. (1885) pp. 233-4. 

 t Amer. Journ. Micr., ii. (1877) pp. 142-3. 



