No. 6. DEPARTMENT OF AGRICULTURE. 456 



found that, wherever the rats were intentionally or unintentionally 

 oxteriuinakHl, the jdajiuc rapidly disappeared; whereas at other 

 places, where too little attention had been paid to the rat plague, the 

 pestilence continued. This connection between the human plague 

 and the rat plague was totally unknown before, so that no blame at- 

 laches to those who devised the measures now in force against the 

 plague if the said nu^asures have proved unavailing. It is high time, 

 however, that this enlarged knowledge of the etiology of the plague 

 be utilized in international as well as in other traffic. As the human 

 plague is so dependent on the rat plague, it is intelligible that pro- 

 tective inoculation and tlie application of antitoxic serum have so 

 little effect. A certain number of liuman beings may have been 

 saved from the disease by that, but the general spread of the pesti- 

 lence has not been hindered in (he least. 



With cholera the case is essentially different; it may, under cer- 

 tain circumstances, be transmitted directly from human beings to 

 other human beings, but its nuiin and most dangerous propagator is 

 water, and therefore, in the combating of cholera, water is the first 

 thing to be considered. In Germany, where this principle has been 

 acted on, we have succeeded for four years in regularly extermina- 

 ting the pestilence (^which was introduced again and again from the 

 infected neighboring countries) without obstruction of traffic. 



Hydrophobia too is not void of instruction for us. Against this 

 disease the so-called protective inoculation has proved eminently 

 effective as a means of preventing the outbreak of the disease in 

 persons already infected, but, of course, such a measure can do noth- 

 ing to prevent infection itself. The only real way of combating this 

 pestilence is by compulsory muzzling. In this matter also we have 

 had the most satisfactory experience in Germany, but have at the 

 same time seen that the total extermination of the pestilence can 

 be achieved only by international measures, because hydrophobia, 

 which can be very easily and rapidly suppressed, is always intro- 

 duced again year after year from the neighboring countries. 



Permit me to mention only one other disease, because it is etiolo- 

 gically vei'y closely akin to tuberculosis, and we can learn not a lit- 

 tle for the furtherance of our aims from its successful combating. I 

 mean leprosy. It is caused by a parasite which greatly resembles 

 the tubercle-bacillus. Just like tuberculosis, it does not break out 

 till long after infection, and its course is almost slower. It is trans- 

 mitted only from person to person, but only when they come into 

 close contact, as in small dwellings and bedrooms. In this disease, 

 accordingly, immediate transmission plays the main part; trans- 

 mission by animals, water, or the like is out of the question. The 

 combative measures, accordingly, must be directed against this close 

 intercourse between the sick and the healthy. The only way to pre- 



