1892.] Some Uses of Bacteria. 987 
SOME USES OF BACTERIA. 
By Dr. H. W. Conn. 
(Continued from Vol. XX VI, page 911.) 
I may now pass to the third branch of my subject and speak 
of the use of bacteria as scavengers in the world. A tree in 
the forest falls to the ground and it lies unmolested. It is at 
first hard, solid and impervious to all of the normal agencies. 
No insects can touch it; they cannot bite the hard wood to any 
extent. It lies there month after month. Little by little it 
begins to soften. 
First the bark begins to get soft and finally falls off. By- 
and-by the wood gets quite soft, so that you can easily cut it, 
and perhaps run a pointed stick into it. Then insects get hold 
of it, and they begin to eat it; they bore tunnels and begin to 
crawl through it. The tree grows softer and softer, and finally, 
as you all know from observation many times, the trunk of 
this tree becomes softened into a mass of brown powder which 
sinks down into the soil and disappears. What has become 
of that tree? A bird dies and falls on the ground, and unless 
some animal comes along to eat the bird you will notice that 
the tissues of the bird very soon begin to undergo changes; 
they begin to soften; gases rise from them; the flesh of the 
bird undergoes the process which we call putrefaction, and that 
putrefaction results in the gradual decomposition of the tis- 
sues. Little by little part of the material passes off into the 
air as gas, and the rest of it sinks down into the soil and the 
bird disappears. What has produced all of these changes? 
Did it ever occur to you to ask what the condition of the sur- 
face of the earth would be at the present time if it were not 
for these processes which we call the processes of decay? 
Suppose there were no agencies which caused the gradual 
softening and destruction of trees and the dead bodies of ani- 
mals. Long since the vegetable and animal life of this world 
would have disappeared, and we should have had the surface 
