THE RENDERINQ OF ANIMALS IMMUNE. 115 



Varieties of Venom Used. 



In this the first portion of the investigation the venoms that have been 

 used are only four in number — those, namely, of the cobra of India (Naia 

 tripucUans), of the Crotalus horridus of America, of a large colubrine snake, 

 probably a species of Diemenia, from South Australia, and of the Spedon 

 hcemachates 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 representative 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.^ 



An essential preliminary to exact investigations with active substances 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 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 

 sulphuric acid an active dry venom was 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 of each venom used should be known, 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. 



Lethal Doses. 



Experiments were made with it on several animals — as the guinea-pig, 

 rabbit, white rat, cat, and the innocuous grass snake of Italy (Tropidonotus 

 natrix). Very considerable differences were found to occur in the minimum 

 lethal dose for each of these animals. For the guinea-pig the minimum lethal 

 dose per kilogramme was O'OOOIS g.; for the rabbit, O'O0024:5 g,; for the white 

 rat, 0°00025 g,; for the cat somewhat less than 0*005 g.; for the kitten (6 weeks 

 old), 0°002 g, ; and for the grass snake the relatively larger dose of 0°03 g, 



^ My supply of cobra venom being much larger than that of any of the cithers, this venom 

 Was chiefly used in the experiments ; and in all of those to be referred to the administration 

 Was effected by subcutaneous injection. 



