DEFENSES OF THE BODY 125 



A case in point is carbolic acid. This substance is 

 always made in at least very small quantities in the 

 human intestine, and on being absorbed into the 

 blood is converted by union with sulphuric acid (in 

 the liver) into a new compound. Now, by virtue of 

 this habitual synthetic defense, the body is able to 

 dispose of much larger quantities of carbolic acid 

 than it is ordinarily called on to get rid of. In a 

 silent way, this is a highly useful defense, for it is no 

 rare occurrence for the intestine to make carbolic 

 acid in quantities injurious to the nervous system 

 and other tissues, were it not for this specific protec- 

 tive power of the cells. And when it occasionally 

 happens that a person recovers from a large poisonous 

 dose of carbolic acid, this recovery is to be placed to 

 the credit of these same synthetic powers that have 

 been called in to operate on a large scale instead of 

 in their habitual more limited way. 



We may regard the oxidative and synthetic 

 defenses as having a relatively simple chemical 

 character, if we compare them with some other 

 protective methods. Various more or less complex 

 biological oxidative procedures may be combined 

 with synthetic processes, but, generally speaking, 

 these methods are not adequate to rid the body of 

 its most dangerous enemies, the pathogenic bacteria 

 and the poisons which they make. For more intri- 

 cate mechanisms are necessary to cope with such 

 invaders, and they are not wanting. Among these 

 there are none more important than the white blood 



