A PRIZE ESSAY. 
87 
them. The one class goes to form fat, or to support 
the natural heat of the body, and passes off by the 
skin in sweat, or in moisture of the breath, and all its 
excess or undigested part goes off in dung. The excess 
of nitrogenous food, all that not required for repairing 
the daily waste of the body, or to increase its growth, 
also passes off in dung, as excrement. This is a small 
portion, and its effects on the strength of dung have 
been pointed out. But the wear and tear, as we may 
call it, of the flesh and blood, the parts which are daily 
and constantly thrown out of the body, as excretions, 
or old materials, enter the circulation, and pass out of 
the body in urine. This is the point to which I would 
call your attention. The undigested food, and the 
excrements not containing nitrogen, go off in dung. 
The food and the spent parts of 'the body, containing 
nitrogen, go off in urine. This last, too, is the course 
of most alkaline salts taken into the body. They pass 
off in urine. Here, then, we come to the subject quite 
prepared to understand it. The urine is a collection 
of salts, some of mineral, others of animal origin. 
But that which gives the urine its peculiar and char¬ 
acteristic properties, is a substance formed from the 
nitrogenous food, and termed urea. Now you need 
hardly trouble yourself to remember this new name; 
all I want you to understand about it is, that when 
urine is exposed to air it rots, and this peculiar sub¬ 
stance is changed to ammonia. That is the point to 
be remembered. In considering urine, therefore, as 
a manure, it will not be necessary to point out further 
the mode of its action, than to refer that of every an¬ 
imal to its salts and power of forming ammonia. The 
quantity of the last will be in proportion to the quan¬ 
tity of urea. There are other salts of ammonia in 
urine, and also mineral salts. These affect but little 
the value of urine as a manure. 
It is the urea, essence of urine, that substance which 
forms ammonia in rotting urine, which alone makes 
this liquid more valuable than dung. Hence, reader, 
