62 UTILIZATION OF MINUTE LIFE. 



photography : by the action of heat it is converted 

 into pyrogallic acid, which is still more useful to 

 photographers. By mixture with salts of iron they 

 produce ink and black dyes, and tincture of galls is 

 a reagent constantly employed in chemical labora- 

 tories. 



These gall-nuts are found upon the leaves of an 

 oak tree (Quercus infectoridj L.) The little red 

 oak balls found in our oak leaves are owed to the 

 Gynips quercusfolii (Fig. 5) ; they also can be em- 



FIG. 5. a, Foreign galls ; b, Gall-nuts of Cynips quercus folii. 



ployed to produce ink, dyes, gallic acid, etc. ; but 

 Berzelius assures us that they contain little more 

 tannic acid than the leaf itself on which they are 

 produced. 



Messrs. Lacaze and Eiche ("Archives des 

 Sciences Physiques et Naturelles de Geneve," xxx. 

 17) have profited by the singular conditions under 

 which the young Cynips are developed in the gall- 

 nuts, to solve an important physiological problem : 



