THEORIES OF IMMUNITY. 



blood as antitoxine). If this process goes on, 

 the T groups may produce their effects, but why 

 do not the thousands of extra T groups produce 

 some result, when it is known that in the begin- 

 ning one minimal lethal dose will do so? 



Many other objections and difficulties are 

 brought forward against the theory, which of 

 course cannot be expected to explain all the 

 phenomena in such obscure reactions as these of 

 which we are speaking, but perhaps the one that, 

 whether valid or not, requires more accurate 

 terminology in those speaking upon the subject, 

 is brought out by the use of the formulae above 

 displayed. The expression is constantly heard 

 that these atom-groups (receptors, side chains, 

 radicals) are produced in the cell in excess, and 

 thrown off to exist free in the blood as the anti- 

 toxine or other antibody, as the case may be. 

 If the chemical reaction can be expressed at all 

 by such a formula as employed above, what is 

 thrown off is a radical — an incomplete sub- 

 stance — and cannot exist free in the blood as 

 would be supposed from the expressions used 

 in regard to it. It is therefore necessary to 



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