48 ADAPTATION AND DISEASE 



curious parallelism with the period of incubation followed by 

 acute disease as seen in bacterial injections. 



We owe to Ehrlich a series of observations which further 

 enforce the parallelism. Feed mice or other small animals 

 upon small non-lethal doses of ricin, and slowly increase the dose, 

 and eventually the animals can be given with impunity one 

 hundred times the fatal dose. Or again, with great care, inoculate 

 the animals subcutaneously with minute but progressively 

 increasing doses, taking care to allow any signs of disturbance 

 to pass away before a new dose is given, and by this means 

 the little animals can be made to stand five thousand times the 

 lethal dose. 



Now the castor oil plant and its poison are not objects which 

 the ordinary European rabbit or mouse is accustomed to 

 encounter. If we take the blood or other body fluids of control, 

 normal, animals we find that they are absolutely powerless to 

 neutralize the poisonous principle. Take on the other hand the 

 blood serum of the treated and immunized animal and mix that 

 blood serum with the lethal dose of ricin, or ten, or a hundred, 

 or a thousand times the lethal dose (according to the grade of 

 immunity induced), and the poison is rendered inert. That is 

 to say, inject the mixture into another animal of the same species 

 and no effects are induced. Clearly in the immunized animal the 

 blood now contains antitoxic substances, bodies which combine 

 with the toxin or break it down, rendering it inert and harmless. 



And these substances have not been produced in the blood, 

 or from the toxin, by some form of chemical activity undergone 

 in the blood itself. Once an animal has been immunized it 

 may be bled and re-bled until many times the normal amount 

 of circulating blood has been removed from it — and notwith- 

 standing the blood continues to be antitoxic. Obviously, in 

 the first place, the antitoxin is produced by the cells of the body, 

 the tissues, or certain of them. Obviously the amount of anti- 

 toxin produced is not in direct proportion to the amount of 

 toxin injected ; in other words, once the cells, stimulated by 

 minute doses of ricin, have acquired the property of elaborating 

 an antiricin, they continue to produce it for weeks and months. 

 The cells have acquired a new power, that of elaborating anti- 

 ricin, and they continue to elaborate and discharge this body 

 long after the original stimulus has disappeared. 



