SCIENCE- G OSSIP. 



DESMIDS. 

 By Dr. G. H. Bryan, F.R.S. 



(Continued fro7ii j>age 259.) 



Transferring to Glycerine. — Desmids cannot 

 be transferred directly from water into glycerine, as 

 the sudden change of density would cause the cells 

 to contract and utterly destroy the form and arrange- 

 ment of the endochrome. There are two methods of 

 effecting the transference sufficiently gradually to 

 avoid damaging the specimens, the first by evaporation 

 trom a dilute solution containing glycerine, the second 

 by osmosis, the glycerine gradually percolating through 

 a thin membrane, and finding its way to the desmids. 

 The method usually recommended and described as 

 Hautsch's method consists in transferring the desmids 

 to a mixture of 3 parts alcohol, 2 parts water, and 1 

 part glycerine, and leaving the mixture freely exposed 

 to the air, but protected from dust till the alcohol 



necessary to evaporate a considerable portion of the 

 water as well ; especially if, as usually happens, a 

 quantity of extra water is introduced with the desmids. 

 And the conditions "freely exposed to the air, but 

 protected from dust," are somewhat incompatible. 



Some desmids, too, notably certain members of 

 the genus Closterium, have a most annoying habit, 

 at the least provocation, of floating on the surface of 

 the fluid. This difficulty occurs in the processes of 

 fixing and cleaning, where it can be obviated by a 

 little care ; but the addition of Hautsch's mixture to 

 the water containing the desmids produces violent 

 circulating currents in the liquid, by which a large 

 proportion of the desmids are carried to the surface. 

 Once Ion the surface the preservative fluid never 



Fie. 3. Closterium striolatuni. 



Fie. 4. Clesttrium < ■ 



[(From photographs by F. Noad Clark.) 



and part of the water has evaporated. If methylated 

 spirit be used for the alcohol, a cloudy opaque mixture 

 will be obtained, which is difficult to clarify either by 

 filtration or by leaving for weeks to settle, and then 

 siphoning the clear liquid from beneath the im- 

 purities which float on its surface. This difficulty 

 could, of course, be prevented by the lavish use of 

 pure alcohol in place of methylated spirit, but 

 seeing that 3 parts of alcohol have to be evaporated 

 for every 1 part of glycerine retained, the method 

 involves a rather extravagant consumption of pure 

 spirit, and a pint will not go far when a quantity of 

 material, including a number of different gatherings, 

 has to be dealt with. Moreover the evaporation is a 

 slow process, as after the alcohol has evaporated it is 



penetrates them properly, and many of the best con- 

 tents of the gathering are lost, h would be desirable 

 to utilise this tendency to float in cleaning gatherings 

 of desmids, if such a method should prove feasible, 

 but the difficulty, once they have floated, is I 

 the desmids immersed again in the water. 



Some American writers have recommended the 

 evaporation of the glycerine from a 10 per Cent, 

 aqueous solution, a still more tedious pri 

 is open to the further objection that even the sudden 

 transference of the desmids into IO per cent, gly 

 may give rise to some contraction of the specimen-. 



The second method was suggested to me by Mr. 

 White, of Litcham, the beauty of whose .-.lides i- 

 sufficient testimony to its advantages. The best plan 



