AIR—SUGAR. 141 
some valuable information, and which deserve to be further 
studied. Drying changes the properties of many drugs. With 
some, peculiar substances first appear during the process of dry- 
ing, while others lose certain principles or acquire a different 
odor (compare also page 15). 
The amount of residue which remains upon drying vegetable 
objects at from 100 to 110° C., until of constant weight, is 
termed the dry weight. Drugs dried at ordinary temperatures 
(about 15° C.) are called air-dried. 
While most parenchymatous cells during life contain, besides 
protoplasm and cell sap, only little or no air (bast-cells, vessels 
and intercellular spaces contain it abundantly), the cells of dry 
drugs are generally more or less filled with air, since upon dry- 
ing this takes the place of water. It is evident from the nature 
of the case that a complete replenishment of the cells with air 
is not perceptible by direct observation. In cells which are 
still succulent and vitally active, on the contrary, and in such 
which are impregnated with liquids for the purpose of examina- 
tion, as is necessary in making microscopical preparations, the 
air bubbles escape as dark rings from the liquid, in consequence 
. of the total reflection of the rays of light. With these the be- 
ginner in microscopical observation soon becomes sufficiently 
acquainted, so as not to mistake them for something else. 
Tissues filled with air (cork, wood) float upon water, notwith- 
standing the fact that the specifie gravity of cellulose and of 
cork is greater than that of water. Tissues free from air (for 
instance, the heart-wood of Guatac), or such from which the air 
is removed, sink in water, as is also the case with thin lamine 
of cork, or with Lycopodium, as soon as the air has been ex- 
pelled therefrom by boiling. 
Of the dissolyed substances contained in the cells the follow- 
ing may yet be considered: 
Sugar is a very widely distributed constituent of drugs. 
Cane-sugar, and the other varieties of sugar, are so abundantly 
soluble in water, and probably also in most cell-juices, that 
even after drying they appear but rarely in a crystallized form 
or otherwise as a solid constituent of the cells. The more spar- 
