ELEMENTARY PARTS OF ANIMAL STRUCTURE. 21 



and insoluble in water and alcohol. It unites with oxygen in defi- 

 nite proportions, so as to form a binoxide and tritoxide. These are 

 formed in the lungs from fibrin, which, in a moist state, possesses the 

 property of absorbing oxygen. The tritoxide, especially, is formed 

 every time that the blood passes through the lungs, and given out 

 again when it returns to the system. A much larger quantity is 

 formed also during the inflammatory condition, constituting the 

 huffy coat. 



Pepsine and Pyin are also included under the head of proteine 

 compounds by some authors, although the existence of this substance 

 in them is denied by many others. The first is a peculiar substance 

 thrown off' from the mucous lining of the stomach, and the second is 

 also a peculiar substance found in pus. Mulder regards it as a 

 protoxide of pi'oteine. Proteine undergoes decomposition very readily 

 when acted on by other chemical substances, especially by alkalies. 

 This is a property which must be continually acting in the living, 

 body ; since the blood is known to have an alkaline reaction. 



Gelatine is the chief constituent of the cellular, or areolar tissue, 

 skin, tendons, ligaments, and cartilages : it is also contained in large 

 quantities in bones. It is obtained by boiling any of the above sub- 

 stances, and allowing the solution to cool. Glue is an example of 

 impure gelatine. It contains no proteine^ hence it has been concluded 

 that it cannot yield albumen, fibrine, or caseine. It is insoluble in 

 cold water, alcohol, and ether, and has a strong affinity for tannin. 

 The process of tanning leather results from this affinity. Proteine 

 cannot be obtained from gelatine, but it is probable that it or its com- 

 pounds have yielded gelatine, for the gelatine of the chick must be 

 produced from a compound of proteine. 



Chondrine resembles gelatine in many respects, except that it is 

 not precipitated by tannin, and yields a precipitate to acetic acid, 

 alum, acetate of lead, and protosulphate of iron, which do not dis- 

 turb solutions of gelatine. It is obtained by boiling the permanent 

 and temporary cartilages ; also from the cornea, and gelatinizes when 

 cool. 



Elaine^ stearine^ and margarine are proximate principles of fat. 

 The first gives fluidity, the second is the solid ingredient, and the 

 third is of medium consistency. Stcarine is but sparingly present 

 in human fat. 



Hcematosine is the red colouring matter of the blood contained in 

 a capsule which is composed of globidine. The latter is regarded 

 by some chemists, as a proteine compound. 



In regard to the secondary organic xompounds^ they are trans- 

 formed by some unknown chemical agency, from the elements of the 

 tissues, to be excreted from the system by particular organs. There 

 is reason also to believe, that, at least with respect to some of them, 



