262 PROCEEDINGS OF THE AMERICAN ACADEMY 



vol. V. p. 61). He proved the possibility of producing it from protein 

 bodies ; but the artificial indigo would be much more expensive than 

 the natural one. In 1878 he obtained small indications of indigo out 

 of phenyl-acetic acid, a product of coal-tar. In 1880 he got indigo 

 out of ciiinamic acid, which is made out of toluol, also contained in 

 the coal-tar. The cinnamic acid was changed by nitric acid into a 

 nitrum combination, and afterwards changed by brom into dibromid. 

 This latter in contact with alkali produces indigo. But this indigo also 

 is more expensive than the natural one. I am not able to find more 

 concerning the production of color in chemical literature. 



All fats contained in animals and plants are glycerids of fat acids. 

 A large series of fat acids consists always of two atoms of oxygen 

 combined with a number of atoms of carbon, and always twice as 

 many atoms of hydrogen. Of these acids the simplest is formic acid, 

 (CHgO.,), which, is common in insects, and also to be found in some 

 plants (Urtica). 



These acids are extensively developed in some insects living to- 

 gether in numerous societies, as in ants and white ants, but, as far as I 

 know, not in bees or wasps. The acid is sometimes much condensed, 

 and if one strikes a hill with the hand, it will smell strongly of acid. 

 If in winter time, when hills are closed outside, and of course the acid 

 in the hill is more concentrated, one tries to work with the fingers 

 into the hill, to collect Myrmecophiles, the tips of the fingers are 

 sometimes affected as if they had been put in very strong acids. The 

 same is stated of tropical species of white ants living in very strongly 

 built hills. The acid is also reported as corrosive for metals. 



Uric acid is largely represented in Arthropods, and only doubtful 

 for Arachnids and Crustacea. To the rich literature about the pres- 

 ence of uric acid in insects, Krukenberg,* p. 28, adds, after his own 

 observations, twenty-eight species. It is not present in Apis melUjica, 

 nor in the excrements and in the rectal glands of Tetrix bi'punctata, 

 of Locusta viridissima, and some other Orthoptera ; also not in some 

 caterpillars and in the larva? of Cimbex variabilis. He never found 

 a species which contained uric aci-d in the fat body, and none in the 

 intestinal canal and in the Malpighian vessels. The insects contain, 

 besides glycogen, leucin, tyrosin, haemoglobin, and peptic-tryptic and 

 diastatic enzyms. 



* C. 'Ft. W. Krukenberg: Vergl. physiolog. Studien an den Kusten d. 

 Adria, 1880, 1881, vol. iii. p. G2. 



