226 MANUAL OF BACTERIOLOGY. 



the mixture is fatal for guinea-pigs. The paralysis which Ehrlich attributes to 

 toxon would be represented, say, by AT 3 . In between the the combinations 

 represented by AT-s. to AT S are all imaginable combinations, a sliding scale 

 of no definite units. 



In other words, while Ehrlich holds that toxin and antitoxin unite in one 

 definite proportion. Bordet holds that they may unite in any proportions, like 

 two different colors of paint mixed together producing any intermediate color 

 with more or less tint of one or other of the original colors. 



The evidence adduced by Bordet for this conception is very abundant and 

 fully repays study. 



Still another theory offered to explain the peculiar behavior of the antitoxin- 

 toxin mixture is advanced by Arrhenius and Madsen, also supported by experi- 

 mental evidence. They also deny the existence of toxon, and look upon a mix- 

 ture of antitoxin and toxin as analogous to an amphoteric mixture of a dilute acid 

 and alkali, or of an acid and alcohol. In such combinations there are com- 

 pounds formed of the two substances, but some of each of the two constituents 

 remains free. An ester is not only a compound formed by an acid and an alco- 

 hol, but it has free alcohol and free acid. Moreover, the ester is constantly 

 changing, some of the alcohol and some of the acid separating and new ester 

 constantly forming again. When first mixed, more ester is formed, and less 

 alcohol and acid are liberated, till a point of dynamic equilibrium is reached, 

 when just as much ester is formed as there are alcohol and acid liberated. Just 

 so in adding toxin to antitoxin: at first more of the two combine than is set free, 

 but after a time a condition of dynamic equilibrium is established, and any 

 additional toxin remains free. 



Briefly stated, these are the three theories which are now advanced by com- 

 petent authorities, and, if these outlines are kept clearly in mind, it will not be 

 difficult to understand the subject as presented in the many medical journals 

 and the many monographs which have appeared on the subject.* 



The ihsoihs of Ehrlich and Bordet in regard to the composition of lysins 

 may also be appropriately discussed in this connection, as it is from the studies 

 of these bodies that many of the ideas in regard to immunity have been developed. 



A lysin contains two substances, a ihermolabile and a thermostabile substance 

 i. e., one readily destroyed by heating at 55 C. for a half-hour, the other resist- 

 ing much higher temperatures. The thermostabile substance is now called by 

 Ehrlich the immune body, the thermolabile the complement, though Ehrlich has 

 used in the past various other names for these hypothetical bodies. Bordet uses 

 the name substance sensibilisatrice for the thermostabile, Ehrlich's immune body, 

 and alexin for the thermolabile or Ehrlich's complement. Both are agreed that 



*A summary will be found in a monograph by Michaelis. Die Bindungsgesetze 

 von Toxin und Antitoxin. Berlin. 1905. Also a special article entitled. 

 Immunity. Journal of the American Medical Association. Nos. 4 el seq. 

 1905. 



