SNAKE VENOMS, THEIR PHYSIOLOGICAL ACTION. 231 



What, then, is this serum, and how and in what doses is it to be 

 administered ? 



You are, no doubt, aware that an animal reacts to the injection or 

 some toxins or poisons, if the dose is not a fatal one, by manufacturing 

 in its body an anti-toxin, that is to say, a substance which is 

 chemically antagonistic to the toxin, and which by combining with 

 the toxin in some obscure way or other forms a substance which is no 

 longer poisonous. This action is, as far as we know, quite specific. 

 Thus the anti-toxin got by injecting an animal with a toxin called A 

 will neutralise that toxin A and not toxin B, no matter how closely 

 allied these two toxins may be to one another. Further, there are 

 only some poisons to which animals react in this way. Among these 

 may be mentioned the poisons manufactured by the diptheria and 

 tetanus bacilli, the vegetable poison abrin and the venom of the Cobra 

 and possibly of other snakes. 



The method, then, of preparing an anti-toxin is to inject an animal 

 with a small non- fatal dose of the toxin to which an antidote is 

 desired. Some small amount of anti-toxin is then prepared by the 

 animal. This enables the animal to stand a larger dose of toxin the 

 next time. In this vray, by gradually increasing the dose of the 

 poison at each injection, and by allowing a sufficient interval of 

 time between each injection for the formation of more anti-toxin, the 

 animal becomes immunised, that is to say, becomes able to stand 

 enormous doses of the toxin, each of which doses would represent 

 many times a single fatal dose for an untreated animal. To get an 

 animal up to this state of immunity requires a long time, six months 

 to a year and in some cases even longer. Calmette takes 18 months 

 to two years to immunise his horses. No one knows how and where 

 the antidote is manufactured. But what is important is, that this 

 antidote is present in considerable quantity in the circulating 

 blood. All that has to be done then is to tap the animal and collect 

 the blood. The blood is allowed to clot, and the clear fluid or serum 

 which exudes from the clot contains the anti-toxin desired. 



Horses being large animals and yielding a large quantity of blood 

 at one time without damage to themselves are, as a rule, the beasts 

 employed for this purpose. You will, perhaps, bo astonished when 

 I tell you that a horse can be bled to the extent of a gallon or more 

 without doing it the slightest injury. 



