24 HUMAN PHYSIOLOGY. 



ALBUMINOIDS. 



The albuminoids constitute a group of substances similar to the 

 proteids in many respects, though differing from them in others. 

 When obtained from the tissues, in which they form an organic 

 basis, they are found to be amorphous, colloid, and when decomposed 

 yield products similar to those of the true proteids. The principal 

 members of the group are as follows : 



(a) Collagen, Ossein. These are two closely allied, if not identical, 

 substances, found respectively in the white fibrous connective 

 tissue and in bone. When the tendons of muscles, the liga- 

 ments, or decalcified bone are boiled for several hours, the 

 collagen and ossein are converted into soluble gelatin, which, 

 when the solution cools, becomes solid. 



(fr) Chondrigen. This is supposed to be the organic basis of 

 the more permanent cartilages. When they are boiled, they 

 yield a substance which gelatinizes on cooling, and to which the 

 name chondrin has been given. 



(c) Elastin is the name given to the substance composing the 

 fibers of the yellow, elastic connective tissue. 



(d) Keratin is the substance found in all horny and epidermic 

 tissues, such as hairs, nails, scales, etc. It differs from most 

 proteids in containing a high percentage of sulphur. 



INORGANIC CONSTITUENTS. 



The inorganic compounds and mineral constituents obtained from 

 the solids and fluids of the body are very numerous, and, in some 

 instances, quite abundant. Though many of the compounds thus 

 obtained are undoubtedly derivatives of the tissues and necessary 

 to their physical and physiologic activity, others, in all probability, 

 are decomposition products, or transitory constituents introduced with 

 the food. Of the inorganic compounds, the following are the most 

 important : 



WATER. 



Water is the most important of the inorganic constituents, as it is 

 indispensable to life. It is present in all the tissues and fluids with- 

 out exception, varying from 99 per cent, in the saliva to 80 per cent. 



