422 HUMAN BIOLOGY 



It would be quite impossible to follow the intricate rami- 

 fications into which this theory has led and which, though 

 not demonstrable in many of its details, is still the most 

 inteIHgent analysis of the conditions that has been offered. 



The body cell is, of course, a complex laboratory in which 

 a great many different chemical processes can take place 

 side by side. Bayhss, summarizing the activities of the cell, 

 describes it as "a complex of substances of varying chemical 

 natures and in various states of aggregation, associated 

 together by forces of surface tension electrically charged, 

 etc. In these, the liquid state enables an elaborate play of 

 forces to take place. Chemical reactions can effectively 

 proceed simultaneously in different parts of the cell, so 

 that there is some mechanism by which one part is tem- 

 porarily isolated from another." It is quite conceivable, of 

 course, that a great many complex reactions of entirely 

 different nature may take place in a heterogeneous system 

 of this kind, separated from each other by semi-permeable 

 surface layers, but it is hard to conceive the mechanism for 

 a train of events in which, let us say, a molecule of horse 

 serum will arouse a specific antibody response which in 

 principle is exactly like, but in specificity distinctly separate 

 from that aroused by a molecule of horse serum into which a 

 methyl or a diazo group has been introduced. Moreover, 

 it must be remembered that after the reaction is over, 

 after antibodies have been produced, have circulated and, in 

 time, have disappeared from the blood stream, the cell 

 still retains an increased reaction capacity for the particular 

 protein molecule with which it has once reacted. This it is 

 impossible to explain on a physicochemical basis, and yet is 

 most easy to demonstrate. For instance, a human being 

 once injected with horse serum will, years later, on the 

 intracutaneous administration of a minute amount of 

 horse serum, react with a rapid formation of a large wheal, 

 whereas in the perfectly normal subject no reaction whatever 

 may take place. And guinea pigs sensitized with horse 

 serum by a single injection may retain a hypersensitiveness 

 that will result in severe distress of breathing, and perhaps 

 convulsions, months after the first injection of horse serum, 

 which in the normal guinea pig had no effect whatever, 



