310 HYPERSENSITIVENESS OR ANAPHYLAXIS 



enunciated a theory very like this in regard to serum anaphylaxis, 

 to be described shortly. 



Other theories might be cited, but there is only one which gives 

 an explanation which is at all satisfactory without introducing many 

 unproved suggestions. It was introduced quite recently by Good- 

 man, and proceeds on lines somewhat similar to those we followed 

 when dealing with the question of immunity to toxins. The cells 

 of the body maybe classified into three groups: (i) The nerve 

 cells essential to life, and with a high degree of affinity for toxin ; 

 (2) cells not essential to life, but with a higher degree of affinity 

 for toxin than the nerve cells possess ; and (3) inert cells without 

 susceptibility to toxin. If a dose of toxin be injected, the second 

 class of cell will have its receptors satisfied first, and any toxin 

 which is left over will then attack the nerve cells, which \ve 

 assume to be the only region w r here it will do harm. A lethal dose 

 of toxin, therefore, is the amount which will satisfy the receptors 

 of the second group of cells and leave enough toxin to injure the 

 nerve cells sufficiently to cause death. Now if a first injection 

 just sufficient to combine with the receptors of Group 2 were 

 given, a very small additional amount would be sufficient to cause 

 death, since it would go straight to the nerve centres. So far the 

 theory is unsatisfactory, since it is simply a theory of summation, 

 and the total amount necessary to cause death, if given in divided 

 doses, should together form the amount necessary if given in one 

 dose, which is very far from being the case. We have seen that 

 _J_ of the " lethal dose " of tetanus toxin may cause death if given 

 in divided doses. To account for this Goodman supposes that the 

 toxin which combines with the non-essential cells may cause a sort 

 of spreading necrosis of the receptors of the latter, or may interfere 

 with their nutrition ; in either case more of these receptors may 

 be destroyed than the toxin actually combines with. If we can 

 imagine one molecule of toxin destroying ten receptors, the animal 

 would become as susceptible as if ten times the dose were given 

 at once. Put in another way, if it takes x molecules of toxin to 

 satisfy the receptors of non-essential cells, and y molecules to 

 combine with those of the central nervous system and kill, then 

 if in the sensitizing dose each molecule of toxin destroys ten 

 receptors, the lethal amount necessary for a second dose would be 



but + a. x we must suppose much larger than a. 



He compares this process with the injury to the excretory 



