ALLERG1A 91 



cessation in the formation of the amboceptors be explained on the 

 basis of the gradual disappearance of the bacteria. 



On the contrary, it is evident that a stimulus has been given which 

 remains operative long after the primary impulse to amboceptor 

 formation has ceased; to return to our simile, the second tuning 

 fork still vibrates, though the first one which gave rise to its vibra- 

 tion has already become quiescent. The animal has coincidently 

 developed a resistance to the organisms in question which is far 

 beyond its original value; it may indeed be absolute so that sub- 

 sequent infection is altogether impossible. This resistance, more- 

 over, in the case of some organisms at least, may be lasting, e. g., 

 the immunity which follows an attack of typhoid fever or of 

 Asiatic cholera in man. 



If the blood of a recently injected animal (using the typhoid 

 bacillus for example) is further examined it will be found that, aside 

 from the resultant bacteriolytic properties, it has developed still 

 other characteristics which the serum of the untreated animal 

 either did not possess at all, or if so, only to a slight extent. For 

 it will be observed that such blood, even though freely diluted, has 

 now the power of causing the arrest of motility and the clumping 

 or agglutination of the corresponding organisms (Widal reaction), 

 and this result, like the production of the bacteriolysins, is not 

 dependent upon the introduction of living bacteria,but may be effected 

 with dead organisms, as well. If, further, analogous experiments 

 are carried out w r ith organisms like the diphtheria or the tetanus 

 bacillus it will be observed that still other changes develop in the 

 body of the infected animal and that bodies here appear in the blood 

 serum which have the power of neutralizing the specific poisons 

 formed by the organisms in question. Then, again, a curious reac- 

 tion develops in animals which have been infected with the tubercle 

 bacillus, for example, for on subsequent injection with certain deriva- 

 tives of this organism (tuberculin) the animal responds with fever 

 while the previously untreated control shows ho reaction whatever. 



Allergia. These various responses in the reaction of the animal 

 to the introduction of bacteria are now recognized as being merely 

 a partial expression of a general biological law^, to wit, that the 

 animal organism invariably responds to the parenteral introduction 

 of foreign cells (i. e., the introduction of cells by other channels 

 than through the gastro-intestinal canal, whether these be of animal 



