and Observations on the component Parts of Membrane. 375 



Nail and hoof, when long boiled, became of a much darker 

 colour. 



The horn-like crust which covers certain insects and other 

 animals, was subsequently examined; the experiments were prin- 

 cipally made on the plates which covered the body of a large 

 African scorpion, and on the common tortoise-shell of the shops. 



The plates taken from the scorpion were not apparently 

 affected, although digested for a long time in boiling distilled 

 water. 



The tanning principle produced no alteration, when added to 

 the water ; but a faint white cloud appeared, upon the addition 

 of nitro- muriate of tin. 



Tortoise-shell, in thin slips and shavings, was digested in a 

 similar manner during three weeks ; but it was only slightly 

 softened; and the water, which had acquired a brownish colour, 

 was but little affected, even by nitro-muriate of tin, which 

 however formed a white cloud.* 



From some previous circumstances, which need not here be 

 mentioned, I was lastly induced to make some similar experi- 

 ments on albumen ; and, as that of the blood is mixed with 

 gelatin, and with the substance called fibrin by the chemists, 

 which in chemical properties appears to be the same as muscu- 

 lar fibre, and as it is with some difficulty that the albumen can 

 be exactly separated from these substances, I preferred the 

 albumen of eggs, as being pure and unmixed ; and, in order 

 that it might be brought into a state in some measure similar 

 to the bodies lately examined, (by which I mean simple inspis- 

 sation,) I dried it, after coagulation, in a vessel which was 



• The crust which covers insects like the scorpion, appears in every respect to be 

 similar to tortoise-shell. 



MDCCC 3 C 



