INTRODUCTION. 



with extraordinary rapidity, acquiring a great size ; 

 and their reproductive system is developed to such 

 an extent, that the germs liberated from a single 

 plant, such as the Puff-ball, almost defy calculation. 

 On this point M. Fries states, that the number is 

 so immense that in a single specimen he has counted 

 10,000,000, so subtle, that they are scarcely visible 

 to the naked eye, and resemble thin smoke, so light, 

 that they are probably raised by evaporation into 

 the atmosphere, and are dispersed in so many ways 

 by wind, water, animals, &c, that it is difficult to 

 conceive a place from which they can be excluded. 

 These fungi have been discovered in Man, producing 

 various obstinate cutaneous disorders ; also in cases 

 of pulmonary consumption, the most frequent source 

 of mortality in these countries. They have been 

 noticed in a species of Polistes, a Wasp of the 

 West Indies, and in the Silk-worm in Italy and the 

 South of France, producing the disease called Mus- 

 cardine, and materially affecting the produce of 

 its invaluable labours. The fungus, in this case, 

 very nearly resembles common mould, rapidly com- 

 municates from one animal to another, and spreads 

 by the extension of its own minute stems and 

 branches ; also by the production of germs, which 

 are introduced into the blood, carried to distant 

 parts of the body, and invariably occasion death. 

 In Fishes, the ravages of this disease have long been 

 noticed, though perhaps they have not obtained all 

 the attention they merit. Thus Mr. Jesse, appa- 

 rently speaking of fresh-water fish generally, re- 



