564 PHYSIOLOGY. 



We may class with the silks, among the useful materials pro- 

 duced by insects, and which is almost of greater importance, the red 

 colouring matter that several species of the genus Coccus present us 

 with. Many of these insects contain within their whole body a very 

 beautiful red colour, which is extracted by acids ; and these admit 

 of being used as a colouring matter for all materials. Among the 

 German species there is one called Coccus Polonicus, which is abun- 

 dant at the roots of Scleranthus -perennis, and which was universally 

 sought, prior to the introduction of the cochineal, as a red colouring 

 matter. Since the introduction of the cochineal, however, which is a 

 species of this genus, known by the name of Coccus cacti, Lin., and 

 which lives upon the leaves of the Cactus coccinellifer, the Polish cochi- 

 neal has lost its importance. A third species also, which is native to the 

 South of Europe, the Coccus Ilicis, which is found upon the branches of 

 the Quercus coccifera, Lin., and which in the middle ages was especially 

 used by the Arabians, who applied the still used name of Chermes to it, 

 has likewise, owing to the more useful Mexican cochineal, been dis- 

 continued. A fourth species of this genus, the Coccus Jicus, Fab. (C. 

 lacca, alior.), which dwells in the East Indies upon Ficus Indica, F. 

 religiosa, and Mimosa cinerea, and which, by puncturing the young 

 twigs of these plants, occasions the exuding of the clammy resinous 

 substance which when dry is known by the name of lac, or gum lac, 

 likewise produces a red colour, which is most concentrated in the eggs, 

 and the use of which has recently increased so much as to threaten 

 equalling that of the cochineal. 



Lastly, the tannin contained in gall-nuts, and which we have above 

 mentioned as a medicament, has been used as a colouring matter, as it 

 forms with iron a black precipitate, that is admirably adapted to this 

 purpose. The ink also, which to the learned is a very important article, 

 is made by the assistance of this acid. The species of galls used for 

 this purpose are of two kinds ; one, the true gall-nut, proceeds from the 

 Cynips gallce tinctorice, which pierces the leaves of Quercus infectoria, 

 Oliv., which causes those smooth spherical excrescences upon them ; 

 the second kind, which are distinguished by being rugose, and of an 

 angular form, are found on the fruit of Quercus cegylops, and are either 

 the fruit itself distorted by the puncture, or merely the scaly cup, 

 which is developed into a gall. The insect which pierces it is, accord- 

 ing to M. von Burgdorf, Cynips qucrcus calycis. Both are found in 

 southern countries, the latter in Greece and in the islands of the 

 Archipelago, and the former in Asia Minor. 



