226 E. D. EVENS ON 



action of sugar on Fehling's solution). The only way to prevent 

 this is to thoroughly wash out the fixing liquid. 



Many solutions containing copper salts have been recommended 

 in the past, of which the best known are Ripart and Petit's (5), 

 Julien's (6), Harris's (7) (8), West's (9), the glycerine-camphor- 

 water-copper-acetate mixture (10). 



My own method consists in fixing the plant for 24 to 48 hours in 

 a solution containing ^/2-3 per cent, formaldehyde (say, 1-8 per cent, 

 formalin), and 0- 1-0-5 per cent, copper acetate. The presence of 

 camphor as sometimes recommended is injurious to the colour. 

 The material should then be well washed for three to four hours 

 in many changes of water and placed in 2Y2-5 per cent, glycerine, 

 together with a crystal of thymol. This is allowed to evaporate 

 in a warm place, the last traces of moisture being removed by 

 placing it in a desiccator over calcium chloride. The object 

 is then mounted in pure glycerine. The strengths of the various 

 solutions and the time of evaporation (two days to two months) 

 must be adjusted by trial in each case so as to prevent shrinkage. 



In the paper (1) by Jorgensen referred to above, it is suggested 

 that zinc acetate might prove to be better than copper acetate 

 for museum specimens of large plants, although the zinc-chloro- 

 phyll compound is not quite as stable as the copper one. I have 

 tried this for algae, mosses, etc., and have found it very satis- 

 factory, the colour being almost identical with that of the fresh 

 plant, while there is less tendency to shrinkage. I now use it to 

 the complete exclusion of the copper method. 



The fixing solution is : 



5 per cent, neutral formalin (2 per cent, form- 

 aldehyde) ...... 10 c.c. 



10 per cent, zinc acetate in thymol water . 1 c.c. 



For delicate objects dilute with an equal volume of distilled 

 water. Fix for two to three days in the dark. It is advisable 

 to wash out the zinc salts with 5 per cent, formalin or distilled 

 water for two or three hours after fixing, when the object may be 

 mounted direct in 5 per cent, neutral formalin or placed in 

 dilute glycerine with a crystal of thymol and allowed to evaporate 

 in the dark as before. Mount in pure glycerine or in glycerine 

 jelly. This method preserves the cell contents well, e.g. it shows 

 the suspended nucleus in Spyrogyra and the cilia of Volvox. 

 There is no doubt that glycerine shows up the green colour 



