462 POPULAR SCIENCE MONTHLY. 



small number of medical men was inadequate to the conflict with a 

 disease so deeply rooted in our habits and customs. Such a conflict re- 

 quires the cooperation of many, if possible of all, medical men, shoulder 

 to shoulder with the State and the whole population, and now the 

 moment when such cooperation is possible seems to have come. I sup- 

 pose there is hardly any medical man now who denies the parasitic 

 nature of tuberculosis, and among the non-medical public, too, the 

 knowledge of the nature of the disease has been widely propagated. 

 Another favorable circumstance is that success has recently been 

 achieved in the combating of several parasitic diseases and that we have 

 learned from these examples how the conflict with pestilences is to be 

 carried on. The most important lesson we have learned from the said 

 experience is that it is a great blunder to treat pestilences according to 

 a general scheme. This was done in former times. No matter whether 

 the pestilence in question was cholera, plague, or leprosy, isolation, 

 quarantine, useless disinfection were always resorted to. But now we 

 know that every disease must be treated according to its own special 

 individuality and that the measures to be taken against it must be most 

 accurately adapted to its special nature, to its etiology. We are entitled 

 to hope for success in combating tuberculosis only if we keep this lesson 

 constantly in view. As so extremely much depends just on this point 

 I shall take the liberty to illustrate it by several examples. 



The pestilence which is at this moment in the foreground of in- 

 terest, the bubonic plague, may be instructive to us in several respects. 

 People used to act upon the conviction that a plague patient was in 

 the highest degree a center of infection, and that the disease was trans- 

 mitted only by plague patients and their belongings. Even the most 

 recent international agreements are based on this conviction. Although, 

 as compared with formerly, we now have the great advantage that 

 we can, with the aid of the microscope and of experiments on animals, 

 recognize every case of plague with absolute certainty, and although 

 the prescribed inspection of ships, quarantine, the isolation of patients, 

 the disinfection of infected dwellings and ships, are carried out with 

 the utmost care, the plague has, nevertheless, been transmitted every- 

 where, and has in not a few places assumed grave dimensions. 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 who suffer from 

 plague-pneumonia — a condition which is fortunately infrequent — are 

 centers of infection, 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 intentionally or unin- 



