162 



ACIDITY 



simpler members are acetic, lactic, pyruvic, and succinic acids. In addi- 

 tion, living cells contain many organic phosphates (Chap. 13) which are 

 strongly acidic because they contain the phosphate group. 



By Life photographer Carl Iwasaki (c) Ti)iie Inc. 

 Fig. 7-1. Sheep eating the halogeton weed, which is poisonous because 

 of its high content of sokible oxalates. One animal has ah-eady died from 

 eating the weed. 



Alkaline substances encountered in biological materials are somewhat 

 less numerous than the acids. Methylamine and trimethylamine are weak 

 bases, which are present in decayed fish and contribute to the unpleasant 

 "dead-fish" odor. The strong base, choline, is found in many tissues, 

 usually as a salt such as the chloride, or combined in more complex forms 

 (phospholipides, p. 97). Other amines found in decaying animal matter 

 are formed through decomposition of amino acids (p. 321). 



CH3NH, 



(CH3)3N 



(CH3)3NCH2CH20H 



CI 



Methylamine Trimethylamine Choline chloride 



All of the bases and acids contained in a tissue contribute to the acidity 

 or alkalinity of that tissue. Acidity (or alkalinity) in biological ma- 

 terials is of two kinds, "total" and "active." 



