ANIMAL FLUIDS AND TISSUES. 671 



Choline (Trimethyl-oxyetJiyl-ammonium hydroxide), N(CH 3 ) 3 .C 2 H 5 O.OH, has 

 been mentioned as one of the ptomaines. It is a colorless fluid of oily con- 

 sistency, has strongly basic properties, and is extremely unstable. By removal 

 of the elements of water choline is converted into the strongly poisonous 

 substance neurine, mentioned on page 620. On the other hand, choline by 

 oxidation is converted into muscarine, a ptomaine even more poisonous than 

 neurine. 



Cholesterin, C 27 H 45 OH. This substance has been classed by 

 physiologists among the fats, because it is greasy and soluble in 

 ether, but its chemical constitution is that of an alcohol. It is found 

 chiefly in bile, but also in blood, nerve-tissue, brain, contents of the 

 intestines, feces, etc. ; its presence in certain vegetables, as pease, 

 beans, etc., has also been demonstrated. Cholesterin combines with 

 fatty acids to form fats. 



Cholesterin crystallizes in colorless, rhombic plates, which are 

 insoluble in water, alkalies, and dilute acids, but soluble in ether. It 

 sometimes forms in the organism solid masses, known as biliary cal- 

 culi or gall-stones, some of which are almost pure cholesterin. 



Cholesterin is an unsaturated, secondary alcohol, and a derivative 

 of the terpenes. 



Reactions of cholesterin: 



1. Place a small quantity of cholesterin on a slide, moisten with a 

 drop of 80 per cent, sulphuric acid, and cover with a cover-glass. 

 Allow a little iodine solution to run in under the cover-glass and 

 examine it with the microscope. The cholesterin crystals pass through 

 many shades of colors, gradually becoming brown or violet or clear 

 blue. 



2. Evaporate, in a shallow porcelain dish, a small quantity of 

 cholesterin Avith hydrochloric acid containing a trace of ferric chloride. 

 A blue residue is formed. 



QUESTIONS. What three kinds of matter are found as constituents of the 

 animal body, and how can they be determined quantitatively? Mention the 

 chief constituents of blood, and state those which predominate in serum and 

 in the corpuscles respectively. What substances cause the clotting of blood, 

 and what explanation can be given ? How may blood-stains be recognized ? 

 What are the characteristics of the different haemoglobins? Describe methods 

 for determining the specific gravity and the alkalinity of blood. How can the 

 proteins of blood-serum be separated ? Mention the principal constituents of 

 muscles, bone, teeth, and hair. State the properties and reactions of creatine 

 and gelatin. What is the composition of glycerin-phosphoric acid, and in 

 what form of combination does it exist in the body? 



