July 5, 1912] 



SCIENCE 



elimination is of an intermittent character. 



The result of studies on the age and sex 

 distribution of carriers indicates that chil- 

 dren are the least, while women are most 

 prone to this condition. The latter fact is 

 noteworthy, since the spread of typhoid 

 fever by carriers engaged in the handling 

 of and preparation of food must be consid- 

 ered as beyond question. The figures 

 which we have showing the relative fre- 

 quency of infection through such carriers 

 vary considerably, owing to the necessarily 

 different conditions prevailing in different 

 regions. Generally speaking, from 4 to 30 

 per cent, of the cases of typhoid fever are 

 traceable to the chronic carrier. In local- 

 ized outbreaks, such as arise in the family, 

 the boarding house, and the like, practically 

 every case may have this origin. 



Essentially the same facts which have 

 been developed in connection with diph- 

 theria and typhoid fever hold true for other 

 diseases, such as influenza, meningitis, 

 pneumonic plague, dysentery and cholera. 

 In the matter of cholera it may not be with- 

 out interest to note that one of the most 

 effective means employed during the past 

 summer to prevent the introduction of 

 cholera into this country was the systematic 

 examination of all third-class passengers 

 coming from infected ports for cholera 

 carriers. 



By far the most interesting and instruc- 

 tive example of a disease carrier is that 

 revealed in connection with Malta fever. 

 The cause of this disease, the Micrococcus 

 melitensis, has been known for twenty-five 

 years, but the real mode of transmission of 

 the disease was not recognized until five 

 years ago. It was then shown for the first 

 time, and quite accidentally, that the goat 

 is really a chronic carrier of the disease 

 organism. The studies of the British Com- 

 mission showed that among the many thou- 

 sand of goats examined on the Island of 



Malta, fully 50 per cent, gave the agglu- 

 tination test, while 10 per cent, were actu- 

 ally secreting the micrococcus in their milk. 

 The existence of the disease among goats 

 was wholly unexpected, but its existence 

 forcibly taught a lesson on the importance 

 of the chronic carrier. 



The disease in the goat was so mild as to 

 pass unnoticed. On recovery, however, the 

 specific germ instead of disappearing be- 

 came localized in the mammary gland and 

 hence appeared in the milk. The use of 

 this milk by man led to his infection with 

 Malta fever. The recognition that this dis- 

 ease was a milk infection enabled the au- 

 thorities, once and for all, to put an end to 

 the tribute paid by the British army and 

 navy. The simplest precaution, the boiling 

 of the goat's milk or its avoidance, was 

 sufficient to put an end to the scourge. 



In many ways Malta fever in man pre- 

 sents a striking analogy to typhoid fever. 

 In both diseases the specific organism per- 

 sists in the body during convalescence and 

 indeed after full recovery. Their con- 

 tinued elimination in the urine and dis- 

 charges indicates a localization in some 

 part of the body. In both infection occiirs 

 by way of the alimentary tract. 



Carriers are by no means restricted to 

 the bacterial diseases, of which but a few 

 have been discussed. They play an even 

 more important part in the propagation of 

 certain protozoal infections. They consti- 

 tute the natural reservoirs of virus and, as 

 such, are chiefly responsible for the con- 

 tinued existence of these diseases. Thus, 

 cattle which have recovered from Texas 

 fever do not show, on microscopical exam- 

 ination of their blood, any evidence of the 

 presence of the parasite, and yet such blood 

 injected into a healthy animal gives rise to 

 the typical disease. The parasite is clearly 

 present, .either in extremely small num- 

 bers, or, what is more likely, in an unrecog- 



