SCIENCE 



[N. S. Vol. XXXVI. No. 914 



important as a knowledge of the germ it- 

 self is the fundamental fact that disease 

 may be conveyed through the agency of 

 apparently healthy insects, lower animals, 

 and even man himself. It is the recogni- 

 tion of this fact, the existence of disease 

 carriers, which has brought about such re- 

 markable results in the fight against mal- 

 aria, yellow fever, Malta fever and many 

 other diseases. Hence a brief outline of 

 our knowledge of this interesting subject 

 may not be out of place. 



It may be well at the outset to state that 

 the term "disease carrier" is applied to 

 animals or persons who, though apparently 

 in perfect health, harbor and eliminate a 

 given disease germ. The fact that the 

 "carrier" is an apparently healthy animal 

 means that the disease may be spread 

 through a wholly unexpected source. The 

 old view of the transmission of disease by 

 contact with the sick remains true, but it 

 is enlarged and supplemented by newer 

 facts. Since more or less direct contact 

 with the apparently healthy carrier, or 

 with the actually sick serves to spread an 

 infection, it is clear that preventive meas- 

 ures must consider the former as well as 

 the latter. 



Strange as it may seem, the existence of 

 certain carriers, though not their import, 

 was recognized in the early days of bac- 

 teriology. Thus, the presence of the mi- 

 crobe of sputum septicemia in the mouths 

 of healthy persons was noted indepen- 

 dently by Sternberg and by Pasteur, in 

 1880, but it was not until several years 

 later that this organism was shown to be 

 the cause of lobar pneumonia. The fre- 

 quent persistence of this organism in the 

 sputum after recovery was observed at an 

 early date. 



An even more striking example was fur- 

 nished with the discovery of the diphtheria 

 bacillus in 1883, for Loeffler not only found 



this organism in the sick, but also in some 

 perfectly healthy children. So contradic- 

 tory to the accepted order of things was 

 this fact that for several years it prevented 

 the full recognition of this germ as the 

 cause of the disease. The more thoroughly 

 this disease was studied, the more it became 

 evident that recovery did not mean an 

 immediate disappearance of the pathogenic 

 microbe. In other words, clinical recovery 

 did not assure freedom from danger to 

 others. The early recognition of this fact 

 led to the establishment of the bacteriologic 

 control of the recovered patient in the forra 

 as it now exists in practise. Two or more 

 consecutive examinations of the throat and 

 nose must yield negative findings before it 

 can be said that the danger of spreading 

 the infection has been overcome. 



The presence of the pathogenic agent in 

 the active stage of the disease is a neces- 

 sary condition; the persistence of such 

 agent during convalescence is more or less 

 to be expected, but the continued existence, 

 at times, of the organism in the individual 

 after complete recovery, and its presence in 

 persons who apparently have never had the 

 disease is somewhat difficult of explanation. 

 The three types thus alluded to are con- 

 veniently designated as (1) convalescent, 

 (2) chronic and (3) healthy carriers. The 

 latter in the majority of cases perhaps in- 

 cludes individuals who, at some time, and 

 unknown to them, have had an attack of 

 the disease; they are therefore virtually 

 chronic carriers. Others, though healthy, 

 may be in the incubation stage and hence 

 develop the disease some days later. 

 Lastly, a third group would include strictly 

 healthy carriers, those who have never had 

 the disease and are only remotely liable to 

 it. Obviously, then, it is difficult to dis- 

 tinguish between these several groups of 

 healthy carriers. 



