178 RELATIONS OF BACTERIA TO DISEASE 



and are apt to be of a severe character. It is not 

 uncommon to find in the bodies of those who have died from 

 chronic wasting disease, collections of micrococci or bacilli in the 

 capillaries of various organs, which have entered in the later 

 hours of life — that is to say, the bacterium-free condition, of 

 the blood has been lost in the period of prostration preceding 

 death. 



The methods by which the natural resistance may be speci- 

 fically increased belong to the subject of immunity, and are 

 described in the chapter on that subject. 



Carriers. — As has been stated, many of the organisms which 

 produce inflammatory and suppurative affections are normally 

 present oh the skin or mucous membranes ; but it has also been 

 established that several of the causal agents of acute infectious 

 diseases, such as typhoid, epidemic meningitis, diphtheria, etc., 

 may flourish on the mucous membranes of individuals in 

 apparent health. Such individuals are known as "carriers," 

 and they play a highly important part in the spread of these 

 infections. It will be shown more fully below that many of the 

 pathogenic bacteria, as regards their morphological and cultural 

 characters, are very similar to, and have apparently sprung from, 

 organisms which are normally present in the sites of the several 

 lesions. Thus the whole typhoid-dysentery group are related to 

 the b. coli, and the meningococci to various Gram-negative dip- 

 lococci which abound in the naso-pharynx. The carrier state 

 may thus be regarded, in a sense, as a return of these organisms 

 to a saprophytic existence. One group of carriers is constituted 

 by those who have suffered from the disease, and in whom the 

 organism persists after recovery, and these are usually designated 

 "temporary." or "chronic" according to the duration of the 

 condition. The -proportion of those who become carriers, and 

 the period of carrying the organisms, vary in different diseases. 

 In cholera, for example, the period is usually comparatively 

 short, whereas in typhoid the organisms not infrequently persist 

 for an indefinite period of time. The other group of. carriers com- 

 prises apparently healthy individuals, who harbour the organisms 

 and are not known to have suffered from the disease. Some of 

 these may really have had a mild attack, but in others there is 

 no evidence of this ; a few subsequently develop the disease, — 

 " precocious '' carriers. In many instances previous contact with 

 a case of the disease can be traced ; this is a usual occurrence 

 with typhoid carriers. On the other hand, no connection of this 

 kind may be discoverable ; for instance, the meningococcus is 

 often found, especially during epidemics, in "non-contacts," the 



