LECTURE VI. <2,55 



powers of converting various kinds of ani- 

 mal matter into a peculiar and very soluble 

 substance, lately recognized and denomi- 

 nated urea. So soluble is it that we may 

 evaporate the water of the urine to a con- 

 siderable degree without precipitating the 

 urea ; and when we add large quantities of 

 water, to urine, the urea will pervade the 

 whole, and be dissolved in it, so as to be 

 distinguishable in every portion by appro- 

 priate tests. Lime removed from our bones, 

 or taken into the circulatino; vessels with 

 our food, becomes also dissolved in the 

 water of the urine by means of phosphoric 

 acid, which the human kidney prepares in 

 so large a proportion, that the superfluous 

 acid will redden the vegetable blue, and 

 dissolve more lime than is usually found in 

 urine. That the phosphoric acid could 

 not exist formally in the blood, but is pre- 

 pared in the secretory vessels of the kidney, 

 must be evident to every one on consider- 

 ation. Yet in herbivorous animals, who 

 take into the circulation a great deal of flint 

 with their food, the urine is rendered alka- 

 line in order to dissolve that kind of earth. 



