PROXIMATE CONSTITUENTS OF THE ANIMAL BODY 47 



is applied only to the compounds of alkalies with the higher fatty acid*. The aeries of 

 alcohols we have just dealt with containing one OH group replaceable by metal* 

 acid radicals are known as monatomic alcohols. If in the molecule of the paraffin 

 or more atoms of hydrogen have been replaced by the group OH, we speak of diatomic 

 or polyatomic alcohols. Thus, derived from the paraffin propane C 3 H 8 we may have 

 the monatomic alcohol C 3 H 7 OH, propyl alcohol, or the triatomie alcohol C 3 H 6 (OH),, 

 which is known as glycerin, or glycerol. 



Other alcohols of physiological importance are cholesterol and cetyl alcohol. 

 Cholesterol is a monatomic alcohol with the formula C 27 H 4B OH. It is very complex in 

 structure, and belongs to the aromatic series. Recent work points to an affinity of 

 cholesterol with the terpenes, which have hitherto been found only as the product of 

 the metabolism of plant cells. Cholesterol is a constant constituent of protoplasm. 

 It occurs in large quantities in the medullary sheath of nerves ; it is a normal con.- 

 ent of bile and may form concretions (biliary calculi) in the gall bladder. In combina- 

 tion with fatty acids it is an important constituent of sebum and of wool fat. 



CH 3 



Another alcohol cetyl alcohol C 16 H 34 = (CH 2 ) 14 occurs in the feather glands of 



C 



H 2 OH 



the duck and forms an important constituent of the wax, spermaceti, obtained from 

 a cavity in the skull of the sperm whale. 



ALDEHYDES. By oxidation of any of the alcohols we obtain another group of 

 compounds the aldehydes. From ethyl alcohol, for instance, by warming with potas- 

 sium bichromate and dilute sulphuric acid, ethyl aldehyde is produced and given off. In 



H 



/H I 



these aldehydes the group C^-H is converted into the group C = 0, and it is the 



|\OH | 



possession of this group which determines the aldehyde character of any compound, 

 as well as the reactions which are typical of this class of compounds. 



Some of the typical reactions of aldehydes may be here shortly summarised : 

 (1) They act as reducing agents, the CHO group being converted into the group 

 COOH, which is distinctive of an acid. We may therefore say that on oxidation 

 aldehydes are converted into the corresponding fatty acids as follows : 



CH 3 CH 3 



CHO COOH 



(ethyl aldehyde) (acetic acid) 



On account of the ease with which this oxidation takes place, aldehydes act as strooj 

 reducing agents. Warmed with an alkaline solution of cupric hydrate th 

 oxygen, reducing the cupric to a red precipitate of cuprous hydrate 

 an ammoniaca! solution of silver (i.e. silver nitrate d^*""* 

 been added until the precipitate first formed is just redissolved) 

 nitrate with the formation of a mirror of metallic silver on the surfo 



nydrazine, they 

 zones and osazones, which are also given by the sugars and 



"t^ "m Edition product, With ammonia, they yield the group of 

 compounds known as aldehyde ammonia. Thus : 



CH 3 CH 3 



+NH 3 = 



