58 NITROGEN. DECOMPOSITION OF NITROGENOUS COMPOUNDS 
products produced in the absence of oxygen are different from 
those produced in its presence, since the former are most likely to 
be of a poisonous nature. These decomposition bacteria occur 
practically everywhere in nature—in the air, in all bodies of water, 
and in extreme abundance in the soil. They are so widely dis- 
tributed and so abundant that they are sure to seize hold of any 
bit of nitrogenous organic matter, which, having become lifeless, 
can serve them as food. Every bit of excreted urea, even that 
secreted by the smallest insects, every dead animal body, every bit 
Zid 
ar [\\ 
Fic. 14.—Proteus vul- Fic. 15.-—-Common 
garvis,a common bacter- decomposition bacteria. 
ium of decomposition. B. fluorescens and B. 
subtilis. 
of vegetable matter whether it be leaf, branch, or fruit, provided it 
contain proper moisture, is sure to be appropriated as food by some 
of these ubiquitous decomposition bacteria. The materialis used 
as food by the microérganisms, and, as a consequence, they mul- 
tiply rapidly within the decaying substances, developing vigorously 
for a time. After they have used up the food, their growth is 
checked and some of them remain ready to grow again when more 
organic matter comes within their reach. By their action, then, 
every bit of organic matter which reaches the soil is seized and 
rapidly decomposed. 
The chemical nature of these destructive changes is very 
complicated and highly varied. It will be a long time before our 
chemists understand them, for they involve problems in physiolog- 
ical and organic chemistry yet unsolved. We know that many 
new products are formed, and that these new products must be 
regarded as belonging to at least two types, so far as concerns their 
