CH. xxv.] ALBUMINOIDS. 4OI 



acid, and we shall have to consider them again in relation to 

 that substance. 



The following diagrammatic way of representing the decom- 

 position of nucleo-proteid will assist the student in remembering 

 the inter-relationships of these substances. 



Nucleo-proteid 



I 

 Proteid Nuclein 



I | 



Proteid Nucleic acid 



Phosphoric acid Purine bases Other imperfectly 



known substances. 



C. ALBUMINOIDS. 



The albuminoids are a group of substances which, though 

 similar to the proteids in many particulars, differ from them in 

 certain other points. The principal members of the group are 

 the following : 



Collagen, the substance of which the white fibres of connective- 

 tissue are composed. Some observers regard it as the anhydride 

 of gelatin. In bone it is often called ossein. 



Gelatin. This substance is produced by boiling collagen with 

 water. It possesses the peculiar property of setting into a jelly 

 when a solution made with hot water cools. It gives most of 

 the proteid colour tests. Many observers state, however, that it 

 contains no sulphur. On digestion it is like proteid converted 

 into peptone-like substances, and is readily absorbed. Though it 

 will replace in diet a certain quantity of proteid, acting as what 

 is called a ' proteid-sparing ' food, it cannot altogether take the 

 place of proteid as a food. Animals fed on gelatin instead of 

 proteid waste rapidly. 



Chondrin, the very similar substance obtained from hyaline 

 cartilage, is a mixture of gelatin with mucinoid materials. 



Elastin. This is the substance of which the yellow or elastic 

 fibres of connective-tissue are composed. It is a very insoluble 

 material. The sarcolemma of muscular fibres and certain base- 

 ment membranes are very similar. 



Keratin, or horny material, is the substance found in the 

 surface layers of the epidermis, in hairs, nails, hoofs, and horns. 

 K.P. D D 



