DUST AND DISEASE. 291 



ill-smelling drains. According to them the matter of epi- 

 demic disease is formed de novo in a putrescent atmosphere. 

 On the other side we have writers, clear, vigorous, with 

 well-defined ideas and methods of research, contending that 

 the matter which produces epidemic disease comes always 

 from a parent-stock. It behaves as germinal matter, and 

 they do not hesitate to regard it as such. They no more 

 believe in the spontaneous generation of such diseases than 

 they do in the spontaneous generation of mice. Pasteur, 

 for example, found that pebrine had been known for an in- 

 definite time as a disease among silk-worms. The develop- 

 ment of it which he combated was merely the expansion of 

 an already existing power, the bursting into open confla- 

 gration of a previously smouldering fire. There is nothing 

 surprising in this ; for though epidemic disease requires a 

 special contagium to produce it, surrounding conditions 

 must have a potent influence on its development. Common 

 seeds may be duly sown, but the conditions of temperature 

 and moisture may be such as to restrict or altogether pre- 

 vent the subsequent growth. Looked at, therefore, from 

 the point of view of the germ-theory, the exceptional energy 

 which epidemic disease from time to time exhibits is not 

 out of harmony with the method of Nature. You some- 

 times hear diphtheria spoken of as if it were a new disease 

 of the last twenty years ; but Mr. Simon tells me that from 

 about three centuries ago, when tremendous epidemics of it 

 began to rage in Spain (where it was named Garrotillo), 

 and soon afterward in Italy, the disease has been well 

 known to all successive generations of doctors ; and that, 

 for instance, in or about 1758, Dr. Starr, of Liskeard, in a 

 communication to the Royal Society, particularly described 

 the disease, with all the characters which have recently 

 again become familiar, but under the name of morbus strait- 

 gulatorius, as then severely epidemic in Cornwall ; a fact 

 the more interesting as diphtheria, in its more modern re- 



