222 



THE FLUIDS. 



udation merely. Fig. 130 shows the relations of the uriniferous 

 tubes, arterial branches, and Malpighian tufts in a section of the 

 kidney ; and Fig. 131 shows two tufts, with their afferent and effe- 



Fig. 131. 



Fig. 132. 



Fig. 131. Relation of Malpighian tufts to the vessels, a. Branch of the renal artery, a/. Afferent 

 vessel, m, m. Malpighian tufts, ef, ef. Efferent vessels, p. Vascular plexus surrounding the 

 tubes, st. Straight tube. at. Convoluted tube. (Magnified about 30 diameters.) 



Fig. 132. Uriniferous tube and its epithelial lining. A. Portion of a secreting tube from the cor- 

 tical substance of the kidney. B. The epithelium or gland-cells, more highly magnified (700 times), 

 c. Portion of a tube from the medullary substance of the kidney. At one part the basement mem- 

 brane has no epithelium lining it. 



rent arteries. Fig. 132 shows a uriniferous tube with its epithelial 

 lining, and, at B, a few cells, derived from its interior, of the scaly 

 epithelium by which the true urine is secreted. 



Uses. Urine is merely an excretion, i. e. it consists essentially 

 either of effete elements resulting from the disassimilation of the 

 tissues, or of others existing in the blood in excess the incessant 

 removal of which is essential to the health of the organism. 



Urinary Deposits. 



Though normal urine is perfectly clear and transparent when 

 first emitted from the bladder, solid matters soon appear in it, form- 

 ing a pellicle on its surface, or a sediment ; and which are called 

 urinary deposits. These are quite numerous, as found in various 

 normal and abnormal conditions, and may be divided into two 

 classes: 1, histological elements; 2, crystalline substances of mine- 

 ral and organic origin. 



I. The histological elements have been specified at the commence- 

 ment of this section, these being of course all suspended in the 

 urine while it is still in the bladder, viz : 



