DUST AND DISEASE. 19 



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 silkworms. The de- 

 velopment of it which he combated was merely the 

 expansion of an already existing power — the bursting 

 into open conflagration of* a previously smouldering lire. 

 There is nothing surprising in this. For though 

 epidemic disease requires a special contagium to pro- 

 duce it, surrounding conditions must have a potent in- 

 fluence on its development. Common seeds may be 

 duly sown, but the conditions of temperature and mois- 

 ture may be such as to restrict, or altogether prevent, 

 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 in 

 harmony with the method of Nature. We sometimes 

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

 but Mr. Simon tells me that about three centuries ago 

 tremendous epidemics of it raged in Spain (where it was 

 named Garrotillo), and soon afterwards in Italy; and 

 that since that time the disease has been well known to 

 all successive generations of doctors. In or about 1758, 

 for instance, Dr. Starr, of Liskeard, in a communication 

 to the Eoyal Society, particularly described the disease, 

 with all the symptoms which have recently again become 

 familiar to us, but under the name of Tnorhus strangula- 

 torius, as then severely epidemic in Cornwall. This fact 

 is the more interesting, as diphtheria, in its more modern 

 reappearance, again showed predilection for that remote 

 county. Many also believe that the Black Death, of 



