1894 - 95 .] Antivcnene and Immunization against Venom. 453 
number, those, namely, of the cobra of India {Naja trijpudians), of 
the Crotalus horridus of America, of a large colubrine snake, 
probably a species of Diemenia, from South Australia, and of the 
Sepedon hannachates of Africa. The venoms are therefore those 
of the most deadly of the poisonous serpents of Asia, America, 
Australia, and Africa, respectively ; and further, they are representa- 
tive of the chief differences that occur in the composition and action 
of venoms, for they are derived from members of the two great 
groups of the colubrine and viperine serpents. 
My supply of cobra venom being much larger than that of any 
of the others, this venom was chiefly used in the experiments ; 
and in all of those to be referred to to-night, the administration was 
effected by subcutaneous injection. 
An essential preliminary to exact investigations with active sub- 
stances must always be the determination of the activity of the 
substances. The only convenient method for doing this is to 
define the smallest dose capable of producing death for any given 
weight of animal — that is, the minimum-lethal dose. The venoms 
in their natural state are inconstant in activity, mainly because of 
variations in the quantity of the water which they contain. The 
cobra venom has, however, nearly always been received in the form 
of a dry solid ; but when this was not so, it has been dried in vacuo 
over sulphuric acid. 
Outside of India, there are few persons skilled in the hazardous 
task of taking venom directly from living serpents. Accordingly, 
with a few exceptions, the other venoms were not received in a 
pure form, but in the form of the dried venom glands. From 
these glands, however, the poisonous constituents may easily be 
extracted with water, and, on evaporating the solution over sul- 
phuric acid, an active dry venom is obtained, containing, however, 
other substances besides those which are active. I am not in a 
position, therefore, to make any statement in regard to the relative 
activity of the different venoms. For the objects in view, what 
only is necessary is that the exact minimum-lethal dose should be 
known of each venom in the state in which it is used, whether it be 
pure or diluted with a certain small amount of inert matter. 
Each of the four venoms was, however, found to be very active, 
but the cobra venom especially so, — a part of the difference between 
