DIPHTHERIA ANTITOXIN 427 



the animal is treated with increasing doses of the particular poison. 

 The toxias, which have been previously tested on small animals, such 

 as rabbits and guinea-pigs, are injected subcutaneously, intramus- 

 cularly, or intravenously. At first either very minute doses of weak 

 toxins, or toxins which had been modified by chemical agents, or in 

 other ways, are employed. In the case of tetanus, in the early stages 

 the toxin is usually modified by being treated with iodine. The 

 injection of the toxin may be followed by swelling at the site of 

 inoculation, loss of appetite, general malaise, and rise of temperature. 

 When these have passed off the animal receives a second, rather 

 larger injection, and in this way the quantity of toxin is increased 

 until within a few months the horse is capable of tolerating many 

 thousand multiples of what would be a lethal dose if given as a first 

 injection. When the serum has reached the strength suitable for 

 chnical use, blood is withdrawn from time to time by venesection. 



It is evident that only healthy horses are of service in pro- 

 viding healthy antitoxin, even as healthy children are necessary 

 in arm-to-arm vaccination. To provide against any serious 

 taint, the horse is tested for glanders (with mallein) and for 

 tuberculosis (with tuberculin). The dose of the injection of 

 toxin is at the commencement about -^ c.c, or a little more. 

 The site of the inoculation is the apex of the shoulder, which 

 has been antiseptically cleaned. After the first injection there is 

 generally a definite febrile reaction and a slight local swelling. 

 From xn- or ^ c.c. the dose is steadUy increased, until at the end of 

 two or three months * perhaps as much as 300 c.c. (or even half a 

 litre) may be injected without causing the reaction which the initial 

 injection of -^^ c.c. caused at the outset. This shows an acquired 

 tolerance of the tissues of the horse to the toxic material. After 

 injecting 500 c.c. into the horse without bad effect, the animal has 

 a rest of four or five days. 



3. To obtain the Antitoxin. — During this period of rest the 

 interaction between the living body cells of the horse and the toxins 

 results in the production in the blood of an antitoxin. By means 

 of a small sterilised cannula, five, or eight, or even ten litres of blood 

 are drawn from the jugular vein of the horse into sterilised flasks or 

 jars. As used in Paris, the top of the jar is closed by two paper 

 coverings before it is sterilised. Then it is again covered with a 

 further loose one. Before use the loose one is removed and replaced 

 by a metal (zinc) lid, which has been separately sterilised. This, 

 metal lid contains an aperture large enough for the tube which 



* To shorten this period Dr Cartwright Wood has adopted a plan by which time 

 may be saved, and 200 c.c. injected, say, within the first two or three weeks. This is 

 accomphshed by using a " serum toxin " (containing albumoses, but not ferments) 

 previously to the broth toxin. 



