262 BOARD OF AGRICULTURE. 



and then replace it, and in a few days examine the tubes 

 again, when we find a growth of mould in the tube from 

 which we removed the cotton and allowed it to remain open 

 for an hour, but there is no growth in the tube in which the 

 cotton has not been disturbed. Experiments like this have 

 been repeated over and over again, and always with the 

 same result. What is the explanation of the fact that the 

 mould grows in the unplugged tube, and also in the one 

 from which we removed the cotton for a short time and then 

 replaced it, and not in the other? Simply this : The air, in 

 getting into the latter tul^e, must pass through the fine 

 meshes of the cotton, and in doing so it is throughly filtered ; 

 every particle of dust and every germ is caught and retained 

 by the fine fibres of the cotton plug, and only pure air is 

 admitted to the tubes with these cotton plugs ; while in the 

 other, the air — carrying many particles of matter, among 

 them the germs of this mould plant — entered without filter- 

 ing, and these germs being so carried and falling upon the 

 piece of moist leather at once begin to grow ; and in the 

 tube from which we removed the cotton for a short time, 

 no growth appeared so long as the cotton remained undis- 

 turbed, because no germs could get into it, as they were 

 arrested by the meshes of the cotton, and we had destroyed 

 by heating any that may have been in the tube when we 

 commenced the experiment ; but, when we removed for a 

 short time the cotton, we allowed the impure air to enter 

 the tube, carrying the seeds of our plant, and so in a few 

 days we find it growing as in the open tube. As I have 

 already said, such experiments as this have been repeated 

 over and over again, and with uniform results, until it is a 

 fact as well established as any in science, that this mould, as 

 well as all other low forms of vegetable life, do not grow 

 spontaneously, — if they grew spontaneously we should 

 have found a growth of mould in the tube in which the cot- 

 ton plug remained as well as in the others in our experi- 

 ments, — but that their seeds or germs are carried from 

 place to place by the air, and when falling on a proper soil, 

 and under proper conditions for their development, they 

 grow and multiply. 



Now, another example of germs being distributed through 



