HAMILTON ^SCIENTIFIC ASSOCIATION. 41 



sorbed into the S3'stem, gives rise to the symptoms of the disease. 

 The germs themselves, however, remain on the throat wall and do 

 not enter the blood stream. Similarlj^ with the germ of lockjaw or 

 tetanus. Now, if after the disease has subsided, we take some of 

 the serum of the patient's blood and mix it with some of the germs 

 causing the disease, we find it has no effect on them whatever. If, 

 however, we mix this serum with some of the toxin secreted by 

 these germs, we find that the toxin is neutralized, i.e., the system 

 has produced an antitoxin, or an antidote to the toxin, and we say 

 the immunity in this case is antitoxic . 



On the other hand in a typhoid infection, the germs first enter 

 the intestine from which they are taken up into the blood stream 

 and by it carried to the various organs of the body, particularly 

 the spleen. They niultipl}^ within these organs and in the blood 

 stream. They carry their poison along with them wherever they 

 go, and liberate it onl)^ when they themselves die or disintegrate. 

 Their poison is not secreted in soluble or diffusible form as was the 

 diphtheria toxin. Now, if in this case, when the attack has sub- 

 sided we take some of tlie serum from the patient's blood and mix 

 with it some typhoid germs, we find that the germs are destroyed 

 but the toxin is not neutralized, i.e., the system has not produced 

 an antitoxin, as in the case of diphtheria, but has rather produced 

 some substance destructive to the bacteria, ie., the immunity is 

 aiitibacterial. Accordingl}^, if a person is naturally immune to 

 diphtheria and typhoid fever we would say he possessed a natural 

 antitoxic immunity in the case of the former, but a natural anti- 

 bacterial immunity in the latter ; or if, having taken these diseases 

 and thereby having acquired an immunity, we would say he pos- 

 sessed an acquired antitoxic immunity for diphtheria, but an ac- 

 quired antibacterial immunity for typhoid fever. 



An immunity may be acquired in two ways. For instance, a 

 child takes diphtheria. His system immediately sets to work to 

 produce an antitoxin to overcome the toxin of the disease. If his 

 constitution is strong enough or if the disease is not too virulent he 

 may .succeed in mastering the infection, and because his ti.ssues 

 have produced the antitoxin by their own activitj', we say he has 



