COMPOUNDS OF ORGANIZATION. 59 



These simple substances have been detected by chemists 

 in the solids and fluids of animals ; but seldom, as we have 

 said, in a free state. Many of them combine, in such va- 

 rious proportions, that it is extremely difficult to determine 

 their true condition, or fix the characters of their natural 

 and permanent results. Without entering into detail, we 

 shall briefly enumerate these various compounds ; the me- 

 thods of procuring them in a separate state ; the characters 

 by which they are distinguished ; and their uses in the ani- 

 mal economy. 



II. COMPOUNDS OF ORGANIZATION. 



1. Gelatine. This substance occurs, in nearly a pure 

 state, forming the air-bag of different kinds of fishes, and 

 well known in commerce under the name isinglass. When 

 in a dry state, it is colourless and translucent ; yields with 

 difficulty to the knife ; and, upon being broken, exhibits 

 a resinous lustre, and conchoidal fracture. 



When thrown into cold water, it becomes soft and in- 

 creases in bulk, but does not readily dissolve. Hot water 

 dissolves it in large quantities. The solution is translu- 

 cent ; of an opal colour ; and gelatinizes as it becomes cold. 

 In this state it is well known by the name of Jelly. Che- 

 mists term it tremulous gelatine. When in a dry state, ge- 

 latine may be kept for any length of time ; but, when thus 

 united with water, it very soon putrifies. Specimens pro- 

 cured from different substances, appear to vary consi- 

 derably, even in the dried state, in the quantity of 

 water which they retain. Those which contain the great- 

 est quantity form the least viscid solutions; while those 

 which contain the least, form solutions which are strong 

 and tenacious. Acids dissolve this substance with facility, 

 and form compounds whose properties have not been exa- 

 mined with much care. Alkalies likewise dissolve it 



