466 Proceedings of Boyal Society of Edinhurgh. [sess*. 
animal which had last received fifty times the minimum-lethal dose 
will survive a larger subsequent dose of venom than an animal 
which had last received only thirty times the minimum-lethal dose. 
It is probable, therefore, that protection depends not only on the 
presence in the body of an antidotal substance, but also on a 
modification in the reaction of the tissues, produced by frequently 
repeated administrations, which lessen the susceptibility of the 
tissues to the injurious action of the venom. 
Antivenene derived^ from the Horse . — Since my former communi- 
cation, also, the blood-serum of the horse, then referred to, has been 
examined. The process of protection had been begun in February 
with one-fifth the minimum-lethal dose, estimated from the results 
obtained in other herbivorous animals. This dose was repeated in 
seven days, and again in five days. One-third the estimated 
minimum-lethal dose was next administered, then, on two occasions, 
one-half, then three-fourths, and then the actual minimum-lethal dose. 
By successive increments, the subcutaneous injections were con- 
tinued until fifteen times the minimum-lethal was administered, four 
months and a half after the protecting process had been commenced. 
Distinct general disturbance, including a rise of temperature, was 
produced by the earlier doses. The later and larger doses, however, 
have produced almost no general reaction, although both the earlier 
and the later doses have caused considerable local effects, and, 
conspicuously, subcutaneous oedema and necrosis of portions of the 
skin. 
Ten days after fifteen times the estimated minimum-lethal dose had 
been administered, blood was taken, with careful antiseptic pre- 
cautions, from the left jugular vein, and a considerable quantity of 
serum has thus been obtained. A small portion of this serum was 
preserved in the liquid state, but the greater part was dried in vacuo 
over sulphuric acid. It yielded 1 1 *5 per cent, of solids in the form 
of a brittle substance, which was easily broken into bright, trans- 
parent, orange-yellow fragments. 
The antidotal properties of this serum have been examined in 
two series of experiments. In the first, the serum, or antivenene, 
was mixed with cobra venom outside of the body ; and in the second, 
cobra venom was injected thirty minutes before the serum. 
In the former series of experiments, it was found that ’005 c.c., 
