VARIOUS FATS 275 



very similar to one another in appearance, there are a 

 very large number of them differing chemically from one 

 another. Thus the fat or oil of dozens of different nuts 

 and plant-products and of lower animals and fishes, and 

 of sheep, oxen, pigs, dogs, elephants, and men contain 

 different and special chemical substances, corresponding 

 to the " cetyl " which is present in the fat of the sperm 

 whale's head. Many of them have acquired as a result 

 of experience and tradition special value for some special 

 purpose. Several oils have peculiar fitness and great 

 value for oiling delicate machinery ; others are used in 

 curing leather, for burning, and for medicinal ointments, 

 whilst a large variety is used as human food. 



