244 The Microscope. 



requires a large amount of alcohol to remove even the excess of 

 the acid it is an expensive reagent to use by those who have to 

 buy their alcohol subject to the exceedingly high tariff of the 

 United States. 



It has many valuable features, however, which render it the 

 most convenient and serviceable of all the many fluids now em- 

 ployed by investigators. 1st, by replacing the fluids of the ob- 

 ject, its penetration is excellent and the tissue is quickly killed; 

 2nd, it preserves well the important features in each case, and 

 no maceration takes place, even if the immersion is unavoidably 

 prolonged; 3rd, it leaves the tissue in good condition for further 

 treatment as it does not produce an insoluble or inorganic 

 precipitate which mechanically interferes with staining, im- 

 bedding, etc. 



CORROSIVE SUBLIMATE. 



A saturated solution in water is made and glacial acetic 

 acid in the proportion of two or three drops to the oz. is added. 

 For round worms, leeches, molluscs, radiates, etc., it is used as 

 above indicated; but for delicate embryos, flat worms, the vis- 

 ceral organs of insects, etc., it may be diluted one-third with 

 water. The object should be placed in a relatively large quan- 

 tity of the fluid and allowed to remain for from ten minutes to 

 one hour, according to the size and nature of the specimen. The 

 alter treatment consists in thoroughly extracting the sublimate 

 from the cells; and to do this well the piece should be placed in 

 slowly flowing water for ten minutes to three hours. The au- 

 thor accomplishes this in the following manner : a s beaker with 

 an overflow is arranged with a syphon to supply it from a higher 

 vessel ; thus a constant current is maintained with no danger of 

 injury to the most delicate tissues. For young embryos, blas- 

 toderms, etc., this serves the purpose well. 



The washing completed the specimen is transferred to 50 

 per cent, alcohol, slightly acidulated with nitric acid, (1 drop to 

 the oz.), for five minutes. The process is completed with pure 

 70 per cent, and then 90 per cent, alcohol. 



This solution of corrosive sublimate may in difficult cases be 

 used warm (60°-70° C) ; it thus kills instantly. 



PERCHLORIDE OF IRON. 



The ordinary alcoholic tincture of iron of the U. S. P. is di- 



