58 THE PRINCIPLES OF IMMUNOLOGY 



Tubes 6-9 are controls to show that normal horse serum is not antilytic, 

 that the laking dose still operates after the preliminary half-hour incubation, 

 and that horse serum itself has no lytic effect. 



Tetanospasmin. For the demonstration of the neutralization of tetano- 

 spasmin by antitoxin and by brain substance, the following experiments are 

 of value. Five guinea-pigs of about 250 grams are needed. 



Pig No. i. Inject five minimum lethal doses of toxin into the thigh muscles. 



Pig No. 2. Mix ten minimum lethal doses of toxin with one unit of 

 antitoxin. Allow to stand at room temperature for about twenty minutes 

 and inject as in pig No. I. 



Pig No. 3. In a sterile mortar grind one-half the fresh cerebrum of a 

 guinea-pig with five minimum lethal doses of toxin, adding salt solution in 

 the smallest amount necessary. Allow to stand two hours, centrifuge and 

 inject the supernatant fluid as in pig No. I. 



Pig No. 4. The other half of a guinea-pig brain is boiled for twenty 

 minutes in water, then ground up with five minimum lethal doses of toxin, 

 allowed to stand two hours, centrifuged, and the supernatant fluid injected 

 as in pig No. i. 



Pig No. 5 serves as a control. 



The guinea-pig injected with toxin will show typical symptoms as de- 

 scribed above, beginning with extension of the leg injected, then showing excita- 

 ble reflexes followed by convulsions, tetanic spasm and death. The antitoxin 

 and fresh brain substance will protect the animals, but the boiled brain will 

 not. The normal animal serves best as a control for the elicitation of 

 excitable reflexes and slight convulsions. 



Route of Absorption of Toxin. It is of interest to note that in 

 man, horse, and guinea-pig the central nervous system alone has 

 the power of neutralizing tetanus toxin, but in the case of the 

 rabbit, liver and spleen in addition have this power. It is main- 

 tained that the gray substance of the nervous system possesses 

 this special affinity, and the white matter does not. Most authorities 

 believe that the toxin is carried along nerve tracks, but Zupnik 

 maintains that it travels through the blood stream and is found not 

 only in the nervous system, but also in the muscles. Studies of 

 Meyer and Ransom and of Marie and Teale indicate that both 

 routes are followed. Depending on the size of the dose, the site of 

 inoculation, and perhaps certain other factors, one or the other 

 route may be followed predominantly, but never to the exclusion of 

 the other. According to Teale and Embleton, the mode of transit 

 along nerve trunks is by way of the axis cylinders and the peri- 

 neural lymphatic vessels. These authors, however, maintain that 

 toxin cannot pass from the choroidal plexis into the cerebrospinal 

 fluid, nor from the capillaries of the central nervous system to the 

 nerve tissues. The special affinity of tetanospasmin for nerve sub- 

 stance is not peculiar and is also exhibited by the neurotoxins of 

 snake venom and by the toxin of bacillus botulinus. Teale and 

 Embleton believe that tetanus antitoxin does not enter the sub- 

 stance of the central nervous system following either intravenous or 

 intrathecal injection, but simply acts by neutralization of the toxin 

 at the site of formation. Clinical experience is not entirely in 

 agreement with the experimental work of these authors, since cases 

 have been improved by the use of serum after tetanic spasms 

 have appeared. 



Therapeutic Use of Tetanus Antitoxin. As is well known, tetanus 



