164 MICROBES AND TOXINS 



blood stream. Cerebral tetanus is more like a mental disease, 

 a sort of delirium, than the systematic tetanic contractions 

 which follow the wound of a limb. In the rat which has 

 received tetanus toxin intracerebrally, the incubation is from 

 forty-eight hours to three days, and if the observer did not 

 know with certainty that he had injected tetanus toxin he 

 would never recognize tetanus in the disease which he observes. 

 Psychical manifestations predominate ; the rat is anxious and 

 vigilant; without apparent cause it is seized with sudden 

 terrors, and runs madly round its cage. . . . During the crisis 

 it seems to obey an internal impulse .... and on careful 

 observation the question forces itself whether many psychical 

 phenomena in man may not also be produced by the fixation 

 on certain nerve cells of bacterial toxins elaborated in the 

 intestine or in some other part of the body at some particular 

 moment (Roux and Borrel).^ 



Selective Fixation of Toxins — For a toxin to kill in 

 the minimum dose it must possess a selective affinity for cells 

 whose function is important, and must proceed to fix itself on 

 these cells and not on others, when introduced into the 

 circulation. Thus it is necessary for a medullary nucleus to 

 attract to itself the few thousandths of a milligram of tetanus 

 toxin introduced into a human body. The intoxication 

 depends entirely on this fixation of the toxin, and it has long 

 been compared to a dyeing process. 



Even in the inorganic world, and among dead substances 

 of animal or vegetable origin, numerous examples exist of 

 the fixation of a substance in solution more dilute even than 

 are the toxins in the blood. The examples which follow are 

 taken from the book of J. Duclaux already quoted. Pre- 



^ In the rat ^^ c. c. of diphtheria toxin subcutaneously does not produce 

 even local oedema, but a rat receiving this dose intracerebrally is soon 

 completely paralysed, and after two or three days of inertia it succumbs. 

 A rabbit of less than 1,500 grams supports perfectly 30 centigrams of a 

 morphine salt injected subcutaneously, whereas i milligram of morphine 

 hydrochloride injected into the brain produces almost immediate effects in 

 a rabbit of the same weight. A tuberculous guinea-pig succumbs when 

 injected intracerebrally with a dose of tuberculin 200 times smaller than 

 when injected subcutaneously. 



