VEGETABLE POWDERS. 



the liquid begins to boil. By this means the starch is gelatinised 

 and all the elements of the seed-coat and pericarp can be distinctly 

 seen. The number of such particles present enables one to judge 

 of the extent to which the sifting has been carried. 



The procedure in the case of medicinal powders is practically 

 the same, but il is advisable to allow the powder to soak in the 

 dilute glycerin for twelve hours. Should starch be found, the 

 shape and size of the grains must be observed, and at the same 

 time the colour of 'the different elements in the powder should be 

 noted. A little of the powder should then be boiled for a few 

 moments in water to which a little caustic potash or soda has 

 been added. After settling, the clear liquid should be poured off 

 and the deposited powder examined, several slides of it being 

 mounted. The treatment with alkali removes any starch that 

 may be present, dissolves colouring matter, etc., and so clears 

 the tissues, the latter effect being enhanced by the better expan- 

 sion of the tissues under the influence of the alkali. 



A strong solution of chloral hydrate (5 parts) in water (2 parts) 

 often yields good service in clearing the tissues ; a little of the 

 powder should be mixed with two or three drops of the reagent 

 and covered with a coverslip ; it should then be raised to the 

 boiling point for a few seconds and cooled. Or a little of the 

 powder may be mixed with the reagent and allowed to stand for 

 twenty-four hours before examination. It must, however, be 

 always borne in mind that delicate markings are less easily seen in 

 solution of chloral hydrate than either in dilute glycerin or 

 water. 



Measurements, when necessary, may be made with an ocular 

 micrometer in the usual way. 



