180 PEACTICAL PHYSIOLOGY 



acid in alcohol, whereby the nucleic acid is precipitated. If this be 

 collected and heated in a closed tube with hydrochloric acid, it splits 

 up into alloxuric bodies and phosphoric acid. There are various forms 

 of nucleic acid, and some of these, e.g. the nucleic acid obtainable from 

 pancreas, contain a carbohydrate in their molecule. 

 C. Haemoglobin. (See blood.) 



CHAPTER V. 

 FATS, FATTY ACIDS, LECITHIN AND CHOLESTERIN. 



THESE bodies are classified together because they are all soluble in 

 ether. After extracting any chopped-up organ or tissue with ether, 

 and evaporating off the ether, a more or less syrupy mass is left 

 behind consisting of a varying mixture of these substances. (See 

 Advanced Course, p. 432.) 



Fatty Acids. These are the end-products of the oxidation of primary 

 monatomic alcohols, 1 aldehydes being formed as an intermediate stage. 

 Thus : 



CH 3 CH 2 OH + O = CH 3 CHO + H 2 0. 



Ethylic alcohol = Acetic aldehyde. 



and then CH S CHO + = CH 3 COOH. 



Acetic acid. 



The ' - COOH ' group is called Carboxyl and the OH of it is replaceable 

 by a metal to form a salt. 



CH 3 COOH + NaOH = CH 3 COONa + H 2 0. 



Sodium acetate. 



If we take the monatomic alcohol containing sixteen carbon atoms and 

 oxidise it, we obtain Palmitic acid (C 15 H 31 COOH), and if we take 

 the eighteenth member we obtain Stearic acid (C 17 H 35 COOH). Both 

 these fatty acids exist in the animal tissues, but they are not present in 

 such large amount as a third one called Oleic acid. This differs from 

 the other two in being derived from an unsaturated alcohol (i.e. an 

 alcohol belonging to the olefine series and in which two of the 

 neighbouring C. atoms are bound together by two valencies). 

 The lowest member of this group of alcohols is allyl alcohol 

 CH 2 = CH - CH 2 OH. Moderate oxidation of this produces its alde- 



T A monatomic alcohol is one containing one -OH or hydroxyl group, e.g. 

 C 2 H 5 OH (ethylic alcohol) ; if it contain three hydroxyl groups, it is called tri- 

 atomic, e.g. C 3 H 5 (OH 8 ) glycerine, and so on. 



