CI1ITIN. 401 



contains the same substance in combination with iodine, sulphur, 

 and phosphorus; and Mulder considers from the analyses of 

 Croockewit that the compound consists of 20 atoms of fibroin, 1 

 atom of iodine, 3 atoms of sulphur, and 5 atoms of phosphorus ; 

 for there were found in sponge l'08% of iodine, 0'50J of sulphur, 

 and 1-90^ of phosphorus, besides the elements of fibroin. 



Preparation. Silk or gossamer threads are boiled with water 

 and strong acetic acid till all albuminous and gelatinous matters are 

 dissolved. The remaining fibroin is then purified in the ordinary 

 manner. 



Physiological Relations. 



This substance has hitherto been only found in the above 

 mentioned secretions of silk-worms and spiders ; physiological 

 investigations show us that it is originally a viscid fluid which is 

 secreted by the spinning vessels of those animals, and hardens on 

 exposure to the air. Under the microscope the fluid mass appears 

 perfectly amorphous. 



Sponge is, as is well known, the dry skeleton of an animal 

 belonging to the Porifera (Grant; and named Sponaia qfficinalis 

 (Linn.) Its chemical constitution affords one of the arguments 

 why the Sponaia should be classed amongst animals and not 

 amongst plants, since in the vegetable kingdom we nowhere meet 

 with a substance in the slightest degree resembling fibroin. 



The physiology of these lower animals has been so little inves- 

 tigated that it is impossible for us to set up an hypothesis regarding 

 the formation of this substance, for notwithstanding the very 

 accurate analyses of Mulder we cannot be regarded as knowing 

 anything of its intimate chemical composition. Mulder's compa- 

 rison of the composition of this body with that of gelatin, can 

 indicate nothing more than the analogy in relation to the physio- 

 logical value of both substances, that is to say, that nature produces 

 in these lower animals a similar group of atoms in order to construct 

 their solid groundwork of tissues possessing little or even no vita- 

 lity The use of this substance is therefore purely mechanical, 



CHITIN. 

 Chemical Relations. 



Properties. This substance, to which Lassaigne gave the name 

 of Entomaderm, is a white, amorphous body, which usually retains 



