ANTITOXINS 3 



and having been tested for purity by microscopic and 

 culture tests is rendered sterile by the addition of 10 

 per cent of a 5 per cent solution of carbolic acid. After 

 48 hours the dead bacilli have settled on the bottom of 

 the jar and the clear fluid is filtered through ordinary 

 sterile filter paper and stored in full bottles in a 

 cold place until needed. Its strength is then tested by 

 giving a series of guinea pigs carefully measured 

 amounts. Less than o.oi cc. when injected hypoder- 

 mically should kill a 250 gram guinea pig. 



Immunizing the Animals. The horses used should 

 be young, vigorous, of fair size, and absolutely healthy. 

 Vicious habits, such as kicking, etc., make no difference, 

 except, of course, to those who handle the animals. 

 The horses are severally injected with an amount of 

 toxin sufficient to kill five thousand guinea pigs of 250 

 grams weight (about 20 cc. of strong toxin). After 

 from three to five days, so soon as the fever reaction 

 has subsided, a second subcutaneous injection of a 

 slightly larger dose' is given. With the first three 

 injections of toxin 10,000 units of antitoxin are given. 

 If antitoxin is not mixed with the first doses of toxin 

 only one-tenth of the doses advised is to be given. 

 At intervals of from five to eight days increasing injec- 

 tions of pure toxin are made until at the end of two 

 months from ten to twenty times the original amount 

 is given. There is absolutely no way of judging which 

 horses will produce the highest grades of antitoxin. 

 Very roughly those horses which are extremely sensi- 

 tive, and those which react hardly at all are the poorest, 

 but even here there are exceptions. The only way, 

 therefore, is at the end of six weeks or two months to 

 bleed the horses and test their serum. If only high 

 grade serum is wanted all the horses that give less 



