The tetanus bacillus manifests other peculiar properties, for some of which it is most difficult to account. Upon susceptible animals it is violently infectious, but is rarely found at any distance from the tissues in which it has first lodged. In laboratory investigations the period of incubation is seldom longer than forty-eight hours. Another peculiarity of the organism is that it generates certain poisons of active properties which may be separated from pure cultures, by whose injection the peculiar spasms of the disease itself may be reproduced. These have been isolated, especially by Brieger, who has given to them the names of _tetanin_, _tetanotoxin_, _spasmotoxin_, etc. It has been estimated that about ¹⁄₃₀₀ Gm. of the pure toxin of tetanus would be a fatal dose for a man. This toxin seems to have a specific affinity for the ganglion cells of the anterior horn of the spinal cord, with which it unites with great force. Herein lies the secret of its disturbing power. It is peculiar that some time may elapse after its injection before the appearance of the first symptoms. Diphtheria toxins appear to be prompt in their action, and thus display quite opposite characteristics. Experiment would seem to show, moreover, that the tetanus toxins do not reach the cord through the blood stream, but appear to slowly pass along the axis cylinders. Sensory nerves do not transport the toxins to the cord. The toxin enters the nerve termination, first of all, at the site of the infection, where it is most concentrated, which will explain why the spasms most frequently begin in the vicinity of the infection, or are the most marked there. Most of the toxin is taken up by the blood and lymph and distributed all over the body, and then passing along the motor fibers it enters the cord and leads to general convulsion. When the toxin is injected directly into the cord the symptoms begin at once. Therefore, for protective purposes, much may be expected from the administration of the antitoxin in cases of suspicious injury or those where experiment has shown there is reason to fear the development of tetanus. There does not appear to be on record a single instance in which a person who had been given antitoxin soon after receiving such a wound has developed tetanus, nor does the antitoxin by itself seem to have done any harm. Obviously, then, the earlier antitoxin is used in the case the better. It may be recalled that there are no diagnostic symptoms of tetanus until the first spasm develops, usually after the expiration of from five to twelve days. By this time the nerve cells are thoroughly saturated with the poison and considerable time may elapse before the antitoxin can reach these cells by a more indirect route.