246 THE MICEOSCOPE. 



they must be transferred to pure water. The nuclei 

 will be seen stained pale violet ; although at first no 

 visible change is produced in the contractile vacuole, 

 later on it assumes a yellowish tint, and finally becomes 

 brown. Double staining may likewise be effected by 

 first using Bismarck-brown for an hour, and then 

 liEematoxylin for a shorter time ; the protoplasm alone 

 remains uncoloured : the difference in colour showing 

 which of the granules are fatty and which are nuclein. 

 The strength of the Bismarck-brown stain should not 

 exceed one in 3,000 or 5,000. A solution of safranine, 

 one of the red aniline dyes, one or two grains to the 

 ounce of water, is an excellent stain and test for amy- 

 loid, starchy matters in unicellular plants. The starch 

 is stained of a fine orange colour, and other portions of 

 a rose colour. 



For bleaching sections before staining Mr. Marsh 

 resorts to the direct action of free chlorine, generated 

 in a pair of Woolf-bottles. 



Fill one of the bottles about two-thirds full of filtered 

 water, and into this place the sections to be bleached. 

 Into the other bottle put a sufficient quantity of crys- 

 tals of chlorate of potash to slightly cover the bottom, 

 and pour upon them a drachm or two of strong hydro- 

 chloric acid. Connect the bottles by the glass tubes, 

 and the yellow vapour of chlorine will be observed to 

 pass into the water contained in the first bottle, and 

 effectually and safely bleach the sections. The time 

 required for bleaching will vary with the nature of 

 the sections operated upon. Decoloration having been 

 effected, the sections must be removed and thoroughly 

 washed to eliminate all trace of chlorine before employ- 

 ing a staining agent. 



Cementing. The following cements are recommended 

 by Mr. Groves for mounting stained preparations : 



Cements. For balsam or glycerine jelly mounts al- 

 most any varnish will do, but for fluids, glycerine, &c., 

 it is necessary to have one tough and which will prevent 

 leakage. The following will be found most efficient : 



]. Mastic and Bismuth. Dissolve gum mastic in 

 chloroform, and thicken with nitrate of bismuth. 



