CRUDE DRUGS. 647 



chu (Acacia), kino (Pterocarpus), rhatany (Krameria) , canaigre 

 {Riimex), tormentilla (Potentilla) and mangrove (Rhisophora). 



Gallic acid crystallizes in silky needles or prisms which are 

 inodorous and possess a faintly astringent taste. It is sparingly 

 soluble in cold water, but soluble in alcohol; forms crystalline 

 compounds with the alkalies, alkaline earths, lead and copper 

 salts ; and gives a bluish-black precipitate with ferric chloride, 

 which is soluble in acetic acid and loses its color on boiling. 



There are three stages in the development of galls correspond- 

 ing to the development of the insect and during which the com- 

 position varies : ( i ) When the galls are first formed and the larva 

 is beginning to develop, the cells of the outer zone, as well as 

 those of the central zone, contain numerous small starch grains. 

 (2) When the insect reaches the chrysalis stage the starch in the 

 cells near the middle of the galls is replaced in part by gallic 

 acid, while the cells at the center and near the periphery contain 

 masses of tannic acid. (3) When the winged insect is developed 

 nearly all of the cells contain amorphous masses of tannic acid 

 with some adhering crystals of gallic acid. After the insect has 

 emerged from the gall the constituents again undergo change, 

 depending largely on the presence of moisture, when the tannic 

 acid is changd into an insoluble oxidation product and the gall 

 becomes more porous, constituting the so-called white gall of 

 commerce. 



Allied Plants. — On a number of species of Rhus, galls due 

 to the stings of certain plant lice (Aphis) are formed, as Chinese 

 GALLS, formed on Rhus semialatcD; Japanese galls, formed on 

 R. japonica, and American Rhus galls, formed on Rhus glabra 

 (Fig. 164) and R. hirta. Chinese and Japanese galls are very 

 rich in fannin, and as they contain less coloring matter than the 

 oak galls are used in the manufacture of gallic acid. They are 

 more or less irregular in shape, but somewhat ovoid, more or less 

 tuberculate, grayish-brown, very hairy, light in weight, brittle. 

 The wall is about i mm. thick, and the cavity contains the remains 

 of numerous insects. 



American nutgalls are formed on Quercus coccinea and 

 Q. imhricaria by Cynips aciculata. When fresh they are globular, 

 1.5 to 3 cm. in diameter, and of a yellowish, somewhat mottled 



