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, 
Tf antitoxin is not mixed with the first doses of toxin 
only oae-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 e.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 borses should contain 
over 300 units, and in about 10 per cent. as much as 
800 units in each cubic centimetre. Very few horses 
