240 RECEPTORS OF THE FIRST ORDER 



the toxins and antitoxins for diphtheria and tetanus. Anti- 

 toxins have been prepared experimentally for a large number 

 of both animal and vegetable poisons, including a number 

 for bacterial toxins. The only ones which, as yet, are of 

 much practical importance are antivenin for snake poison, 

 (not a true toxin, however, see p. 252), antipollenin (sup- 

 posed to be for the toxin of hay fever) and the antitoxins 

 for the true bacterial toxins of Bacterium diphtheriw and 

 Bacillus tetani. 



The method of preparing antitoxins is essentially the same 

 in all cases, though differing in minor details. For commer- 

 cial purposes large animals are selected, usually horses, so 

 that the yield of serum may be large. The animals must, of 

 course, be vigorous, free from all infectious disease. The 

 first injection given is either a relatively small amount of a 

 solution of toxin or of a mixture of toxin and antitoxin. 

 The animal shows more or less reaction, increased temper- 

 ature, pulse and respiration and frequently an edema at the 

 point of injection, unless this is made intravenously. After 

 several days to a week or more, when the animal has recov- 

 ered from the first injection, a second stronger dose is given, 

 usually with less reaction. Increasingly large doses are 

 given at proper intervals until the animal may take several 

 hundred times the amount which would have been fatal if 

 given at first. The process of immunizing a horse for diph- 

 theria or tetanus toxin usually takes several months. Varia- 

 tions in time and in yield of antitoxin are individual and 

 not predictable in any given case. 



After several injections a few hundred cubic centimeters 

 of blood are withdrawn from the jugular vein and serum 

 from this is tested for the amount of antitoxin it contains. 

 When the amount is found sufficiently large (250 "units" 

 at least for diphtheria per c.c.) then the maximum amount 

 of blood is collected from the jugular with sterile trocar and 

 canula. The serum from this blood with the addition of an 

 antiseptic (0.5 per cent, phenol, tricresol, etc.) constitutes 

 " antidiphtheritic serum," or "antitetanic serum," etc. All 

 sera which are put on the market must conform to definite 

 standards of strength expressed in "units" as determined 



