ACTION OF THE TOXIN. 387 



Whatever the nature of the toxin is, it is undoubtedly one 

 of the most powerful poisons known. Even with his probably 

 impure toxalbumin Brieger found that the fatal dose for a mouse 

 was .0005 of a milligramme. If the susceptibility of man be 

 the same as that of a mouse, the fatal dose for an average adult 

 would be .23 of a milligramme or about 2^oo tns f a grain. 



With regard to the action of the toxin it has been shown to 

 have no effect on the sensory or motor endings of the nerves. 

 It acts solely as an exciter of the reflex excitability of the motor 

 cells in the spinal cord. The motor cells in the pons and 

 medulla are also affected, and to a much greater degree than 

 those in the cerebral cortex. When injected subcutaneously 

 the toxin probably to a certain extent is absorbed into the 

 sheaths of the nerves, and thence finds its way to that part of 

 the spinal cord from which these nerves spring. This explains 

 the fact that in an animal often the tetanic spasms appear first 

 in the muscles of the part in which the inoculation has taken 

 place. It is doubtful whether such absorption takes place in 

 tetanus arising naturally in man. In artificial injection of toxin 

 part finds its way into the blood stream, and if infected animals 

 be killed during the incubation period there is often evidence 

 of toxin in the blood and solid organs. Rarely, however, during 

 this period, and probably never after symptoms have begun, is 

 there free toxin in the central nervous system. In the guinea- 

 pig there is little doubt that tetanus toxin has an affinity solely 

 for the nervous system. In other animals, such as the rabbit, 

 an affinity may exist in other organs, and the fixation of the 

 poison in such situations may give rise to no recognisable symp- 

 toms. In such an animal as the alligator, it is possible that 

 while some of its organs have an affinity for tetanus toxin its 

 nervous system has none. These facts are of great scientific 

 interest, and a possible explanation of them will be. discussed in 

 the chapter on Immunity. If tetanus toxin be introduced into 

 the stomach or intestine, it is not absorbed. It to a large extent 

 passes through the intestine unchanged. Evidence that any 

 destruction takes place is wanting. 



Toxin in the Circulating Blood. A research .of far-reaching importance 

 upon the amount of tetanus toxin circulating in the blood of horses infected 

 with the disease has just been completed by Bolton and Fisch of St. Louis. 

 It was undertaken as a result of an inquiry into a number of -fatal cases of teta- 



