SANITARY SUGGESTIONS. 97 



it so, that each class of insects derives its nutriment 

 from the putrescence which surrounds it ? 



161. Do animalcules which exist in the atmosphere 

 derive their nutriment from the vapours which arise 

 from vegetable or animal matters in a state of putre- 

 faction or decomposition ? and if so, were all vege- 

 table and animal matters buried beneath the surface 

 of the ground the instant the vegetative principle of 

 the one, and the vital principle of the other had 

 departed from them, or before decomposition had 

 begun to take place, would atmospheric diseases 

 cease to prevail? 



162. How is it that swarms of insects are ob- 

 served to maintain the same position in the atmo- 

 sphere, without any perceptible movement either to 

 the one side or to the other ? Is it from this cause 

 In the atmosphere where the insects swarm, there is an 

 escape of vapour from beneath, arising from vegetable 

 or animal matter in a state of decomposition, from 

 which vapour those insects derive their nutriment ? 

 Upon one occasion we observed a swarm of insects 

 hovering above a piece of cloth which had been 

 steeped in fatty matter ; the insects maintained their 

 position above the cloth for such a length of time, 

 that we could not avoid the inference that the posi- 



H 



