360 BACTERIOLOGY. 



kicking, etc., make no difference, of course, except to 

 those who handle the animals. A number of such 

 horses are severally injected with an amount of toxin 

 sufficient to kill five thousand guinea-pigs of 250 

 grammes' weight (about 20 c.c. 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 horses that give less than 

 150 units per c.c. are discarded. If moderate grades 

 only are desired, all that yield 100 units may be 

 retained. The retained horses receive steadily in- 

 creasing doses, the rapidity of the increase and the 

 interval of time between the doses (three days to one 

 week) depending somewhat on the reaction following 

 the injection, an elevation of temperature of more than 

 3 F. being undesirable. At the end of three months 

 the antitoxic serum of all the horses should contain 

 over 300 units, and in about 10 per cent, as much as 

 800 units in each cubic centimetre. Very few horses 



