174 MOSSES AND LIVERWORTS 



to say, is used as a germ-destroyer. I am inclined 

 to think, however, that owing to the jelly having 

 to he melted by heat, and often remaining in that 

 condition for some considerable time, the carbolic 

 acid is apt to evaporate. On this account I not 

 unfrequently add a very minute quantity of the 

 acid (just as much as will adhere to the end of a 

 thin glass rod drawn to a fine point is quite 

 sufficient) to the pool of liquid jelly on the glass 

 slip before the specimen is put into it. Quite re- 

 cently, at the suggestion of a friend, I have been 

 using bichloride of mercury (corrosive sublimate) 

 in the same way, and have also substituted twenty- 

 five drops of it for the carbolic acid mentioned 

 in the recipe, when making the jelly. This is, 

 of course, a most powerful germ-destroyer, and it 

 is not liable to evaporate like the carbolic acid ; 

 but it must be used with considerable care, as if 

 too large a quantity is introduced into the jelly a 

 slight precipitate of calomel will be the result, 

 and this will give a cloudy appearance to the cell. 

 With a five-per-cent. solution it is sufficient if the 

 tip only of the pointed glass rod is dipped in, and 

 the small amount thus abstracted is transferred to 

 the melted jelly, and quickly mixed with it. I 

 have frequently also used formalin in the cells for 

 a like purpose; but though it has the effect of 

 solidifying the gelatine to such an extent that it 

 is practically impossible to remelt the jelly, yet 

 this is often a distinct disadvantage should it be 



