144 COMPARATIVE PHYSIOLOGY. 



In consequence, C, H, O, N, are the elements found in great- 

 est abundance in the body. 



The elements S and P are associated with the nitrogenous 

 carbon compounds ; they also form metallic sulphates and phos- 

 phates. 



CI and F form salts with the alkaline metals Na, K, and the 

 earthy metals- Ca and Mg. 



Fe is found in hoemoglobin and its derivatives. "* 



Protoplasm, when submitted to chemical examination, is 

 killed. It is then found to consist of proteids, fats, carbohy- 

 drates, salines, and extractives. 



It is probable that when living it has a very complex mole- 

 cule consisting of C, H, O, N, S, and P chiefly. 



Proximate Principles. 



Proteids. 



1. Organic. 



I (a) Nitrogenous. | Ce?tein'orystalline bodies. 



I (b) Non-nitrogenous. | FaS"'''^''™*^'' 



„ T ■ ( Mineral salts. 



2. Inorganic, j ^^jg^ 



Salts. — In general, the salts of sodium are more characteris- 

 tic of animal tissues and those oi potassium of vegetable tissues. 

 ■ Na CI is more abundant in the fluids of animals ; K and 

 phosphates more abundant in the tissues. 



Earthy salts are most abundant in the harder tissues. 



The salts are probably not much, if at all, changed in their 

 passage through the body. 



In some cases there is a change from acid to neutral or 

 alkaline. 



The salts are essential to preserve the balance of the nutritive 

 processes. Their absence leads to disease, e. g., scurvy. 



GENERAL CHARACTERISTICS OF PROTEIDS. 



They are the chief constituents of most living tissues, includ- 

 ing blood and lymph. 



The molecule consists oi a great number of atoms (complex 

 constitution), and is formed of the elements C, H, N, 0, S, and P. 



All proteids are amorphous. 



All are non-diffusible, the peptones excepted. 



They are soluble in strong acids and alkalies, with change of 

 properties or constitution. 



In general, they are coagulated by alcohol, ether, and heating. 



