Protoplasm. 27 



an acid or an alkali, and receive the names of acid-albumi- 

 nates and alkali-albuminates according to the nature of the 

 agent employed to bring about the alteration. 



Albuminoids very closely resemble proteids in general 

 appearance and in chemical composition, save that some 

 albuminoids contain no sulphur. They differ, however, in 

 one point ; they cannot be made use of by animals as. food, 

 on account of their sparing solubility in water and in the 

 comparatively weak acids and alkalies of the organism. As 

 examples may be mentioned mucin, the substance which 

 gives the viscidity to saliva, gelatin, a familiar commercial 

 product, and keratin, the chief constituent of horn, hoof, 

 nail, hair, and such like. 



B. Amyloids or carbohydrates. These substances, 

 when compared with the group of proteids, are compara- 

 tively simple in their chemical composition. They consist 

 of the three elements carbon, hydrogen, and oxygen, 

 the hydrogen and oxygen being present in the same pro- 

 portion as that in which they occur in water, i.e. two atoms 

 of hydrogen to one of oxygen. The large amount of carbon 

 and hydrogen in their composition gives them their name of 

 carbohydrates, whilst a synonym of starch, viz. amylum, 

 which is one of the chief carbohydrates, accounts for the 

 term amyloid as applied to them. They are sweet to the 

 taste, e.g. sugar, or are capable of being converted into 

 sugar by treatment with a weak acid, or certain other sub- 

 stances found in the plant and animal organism. In addi- 

 tion to ordinary sugar and starch, glycogen or animal 

 starch, milk sugar or lactose, muscle sugar or inosite, may 

 be cited as examples of carbohydrates found in the animal 

 world. 



C. Fats and fatty acids. These substances are closely 

 allied in chemical composition to carbohydrates, from which 

 they are partly derived. They are also largely formed by a 

 transformation of proteids. They contain carbon, hydrogen, 

 and oxygen, usually in the form of more complex molecules 



