356 PROTECTIVE INOCULATIONS. 
cubic centimetres—which had been exposed for one hour to a temper- 
ature of 60° C. At a temperature of 65° C. both the toxic and the 
immunizing action is destroyed. 
Behring (1892) gives the following account of a method which he 
has successfully employed for producing immunity in large animals— 
especially in horses: A culture of the tetanus bacillus is made, in 
bouillon, of such toxic potency that 0.75 cubic centimetre will kill a 
rabbit in three or four days. To two hundred cubic centimetres of 
this culture he adds carbolic acid in the proportion of 0.5 per cent for 
the purpose of preserving it. The horse first receives a subcutaneous 
injection of ten cubic centimetres of this culture fluid to which ter- 
chloride of iodine (ICIl,) has been added in the proportion of 0.25 
per cent; at the end of eight days twenty cubic centimetres of the 
same mixture are given; again in eight days the dose is repeated; 
then, after an interval of three days, thirty cubic centimetres of the 
same mixture. Following this, at an interval of eight days, he gives 
two injections of thirty cubic centimetres each of a mixture containing 
one-half the quantity of ICI, (0.175 per cent). The proportion of 
the iodine terchloride is then reduced to 0.125 per cent, and two 
doses of twenty cubic centimetres each are given. Finally the culture 
fluid is administered in the dose of 0.5 cubic centimetre, and this dose 
is doubled every five days. Before giving the first dose of culture 
fluid without the addition of ICI,, the immunizing value of the blood 
serum of the horse is tested on mice, and if it falls below 1:100 a 
dose of 0.25 cubic centimetre is given instead of the larger dose (0.5 
cubic centimetre) above mentioned. 
Schitz (1892) has applied Behring’s method to a considerable 
number of horses and sheep, and arrives at the conclusion that it is a 
reliable method of protecting these animals against infection with liv- 
ing tetanus bacilli and against the toxic action of filtered cultures; 
that the degree of immunity and the antitoxic power of the blood 
serum increase as larger doses are gradually given. According to 
Behring the immunizing value of blood serum from a horse treated in 
this way is very high. As tested on mice it may be 1:200,000, or even 
more. According to his calculations a serum having a value of 1:100,- 
000, as tested on mice, should be given to a man weighing fifty kilo- 
grammes in the quantity of fifty cubic centimetres, given in the course 
of two days, in order to insure immunity. 
The same author in a subsequent paper (1892) gives details as to 
the method of estimating the therapeutic value of serum from an im- 
mune animal. He first calls attention to the fact that the only re- 
agent by which the antitoxic potency of this serum can be tested is 
