294 THE NEW WORLD OF SCIENCE 



the patient recovers, the conditions are quite the opposite, the 

 causative organism, after the height of the disease is passed, 

 tends to disappear from the blood stream and then from the 

 body, and in most infections it is necessary to make the usual 

 bacteriological examinations early in the course of the disease 

 in order to be successful in isolating it. Sooner or later, there- 

 fore, there comes a time when the infecting organism is unable 

 to survive in the combat with the defensive forces of the body, 

 and it disappears completely. We know, however, that there 

 are many mild cases in all the infectious diseases, from which, 

 nevertheless, the specific organism may be recovered. Here, 

 also, the germs usually disappear completely with recovery. 

 The next step, from the mild case to the healthy carrier is an 

 easy one ; at first glance it sounds paradoxical to speak of this 

 condition as an infection because there are no symptoms of 

 illness. Yet, if we accept the presence of immunity to a new 

 infection and of specific anti-bodies in the blood as evidence of 

 the invasion of the body we must consider the healthy carrier 

 as a person who suffers from the mildest form of infection. 

 Even in this case the normal course of events leads to the 

 gradual disappearance of the infectious agents from the body 

 and the usual healthy carrier is merely casually or temporarily 

 in that condition. 



In certain persons, however, the organism continues to exist 

 in the body for an indefinite period, sometimes for years or 

 even for the remainder of his life, and he is then classed as a 

 chronic carrier from whom the pathogenic organism can be 

 obtained either constantly or at intervals. 



The temporary carrier frees himself from the invading bac- 

 teria by developing an immunity with a surplus of anti-bodies 

 in his body fluids sufficient to kill off the invaders. Why does 

 this not occur also in the chronic carrier? Is the difference due 

 to the microorganism or to the host ? Many investigators have 

 examined the bacteria isolated from such cases, without being 

 able to establish any regular or constant peculiarity of carrier 

 organisms. They seem to vary in the same way and to the same 



