Jounial of Agriculture. [8 Feb., 1907. 



action of superheated steam, break up into glycerine and fatty acids ; the 

 same decomposition can occur through the action' o'f bacteria or of a special 

 ferment found in the mammalian bowel. When fats are boiled with an 

 alkali, glycerine is produced, whilst the fatty acid unites with the alkali 

 to form a soap. 



Of the many fatty acids known to the chemist only some five need be 

 mentioned here — 



Stearic acid which is solid at ordinary temperatures. 



Now — 



Stearic acid united to glycerine gives the fat stearin 



Palmitic acid ,, ,, ,, ,, palmitin 



Oleic acid ,, ., ,, ,, olein 



Caproic acid ,, ,, ,, ,, caproin 



Butyric acid ,, ,, ,, ,, butynn 



Fats, as they occur in the body, contain always two or more of the fats 

 above given, mixed together. Stearin and palmitin, when mixed, often go 

 by the name of margarin, and the more of these two a fat contains the more 

 solid will it be. On the other hand, olein, caproin and butyrin are liquids, 

 and the larger the amount in which they are present the more fluid will be 

 the fat. For instance, suet is chiefly composed o'f stearin and palmitin ; 

 olive oil contains olein as its chief ingredient, whilst milk fat or butter con- 

 tains a considerable proportion of butyrin as well as some of the solid fats. 



When a fat gets rancid what happens is that, through the agency of 

 bacteria, the fat is split up into glycerine and fatty acid, the latter being 

 readily detected by its odour — the smell of rancid butter, for instance, 

 being due largely to butyric acid. In addition to this there is a slitrht 

 oxidation of the liberated fatty acid and the consequent formation of otiiir 

 bodies which are not only odorous, but also harmful to the body when 

 taken in food. 



An interesting property of fats may be referred to here. When a liquid 

 fat is shaken up with sodium carbonate it forms an emulsion exactly the 

 same as if it had been shaken with soap. The reason 'for this is that in 

 most fats there is always a small amount of free fatty acid which unites 

 with the alkali in the sodium carbonate to form a soap, and it is this small 

 amount of soap that conditions the emulsion. 



Lipoid. — Lipoid is a substance found in the wall and in the protoplasm 

 of every living animal cell, it forms the envelope of the red corpuscles of 

 the blood, and also makes up the chief bulk of the myelin or insulating 

 material of nerves. It possesses much the same solubilities as fats (soluble 

 in ether, chloroform, and hot alcohol), but differs from, them in this, that 

 it can absorb water, and though not dissolving in the water, can mix with 

 it. As a constituent of the cell wall, it carries out a most important func- 

 tion in controlling the permeability of the wall, allowing some bodies 

 through more readily than others. Lipoid is composed of a variable mix- 

 ture of at least two substances, lecithin and cholesterin. Lecithin is in 

 reality a modified fat. Whilst fat contains carbon, hydrogen and oxygen, 

 lecithin contains carbon, hydrogen, oxygen, nitrogen and phosphorus, and 

 Is in consequence often spoken of as a phosphorized fat. Lecithin can be 



