150 FRAGMENTS OF SCIENCE. 



five centuries ago, has disappeared as mysteriously as it 

 came ; but Mr. Simon finds that it is believed to be 

 prevalent at this hour in some of the north-western 

 parts of India. 



Let me here state an item of my own experience. 

 When I was at the Bel Alp in 1869, the English 

 chaplain received letters informing him of the breaking 

 out of scarlet-fever among his children. He lived, if I 

 remember rightly, on the healthful eminence of Dart- 

 moor, and it was difficult to imagine how scarlet-fever- 

 could have been wafted to the place. A drain ran close 

 to his house, and on it his suspicions were manifestly 

 fixed. Some of our medical writers would fortify him 

 in this notion, and thus deflect him from the 'truth, 

 while those of another, and, in my opinion, a wiser 

 school, would deny to a drain, however foul, the power 

 of generating de novo a specific disease. After close 

 enquiry he recollected that a hobby-horse had been 

 used both by his boy and another, who, a short time 

 previously, had passed through scarlet-fever. 



Drains and cesspools, indeed, are by no means in 

 such evil odour as they used to be. A fetid Thames 

 and a low death-rate occur from time to time together 

 in London. For, if the special matter or germs of 

 epidemic disorder be not present, a corrupt atmosphere, 

 however obnoxious otherwise, will not produce the 

 disorder. But, if the germs be present, defective drains 

 and cesspools become the potent distributors of disease 

 and death. Corrupted air may promote an epidemic, 

 but cannot produce it. On the other hand, through 

 the transport of the special germ or virus, disease may 

 develop itself in regions where the drainage is good and 

 the atmosphere pure. 



If you see a new thistle growing in your field, you 

 feel sure that its seed has been wafted thither. Just as 



