CONGRESS ON TUBERCULOSIS. 
443 
sions. Why this has happened we know very well, owing to 
the experience quite recently gained as to the manner in which 
the plague is transmitted. It has been discovered that only 
those plague patients that suffer from plague-pneumonia—a 
condition which is fortunately infrequent—are centres of infec¬ 
tion, and that the real transmitters of the plague are the rats. 
There is no longer any doubt that, in by far the majority of the 
cases in which the plague has been transmitted by ocean traffic, 
the transmission took place by means of plague among the ship 
rats. It has also been found that, wherever the rats were inten¬ 
tionally or unintentionally exterminated, the plague rapidly dis¬ 
appeared ; 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 attaches to those who 
devised the measures now in force against the plague if the said 
measures 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 hu¬ 
man plague is so dependent on the rat plague, it is intelligible 
that protective inoculation and the application of antitoxic se¬ 
rum have had so little effect. A certain number of human be¬ 
ings may have been saved from the disease by that, but the 
general spread of the pestilence has not been hindered in the 
least. 
With cholera the case is essentially different ; it may, under 
certain circumstances, be transmitted directiy from human be¬ 
ings to other human beings, but its main 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 exterminating the pestilence (which was in¬ 
troduced again and again from the infected neighboring coun¬ 
tries) without any obstruction of traffic. 
Hydrophobia, too, is not void of instruction for us. Against 
this disease the so-called protective inoculation proper has 
proved eminently effective as a means of preventing the out¬ 
break of the disease in persons already infected, but, of course, 
such a measure can do nothing 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 
