184 CLINICAL DIAGNOSTICS. 



Occasionally hemoglobin and methemoglobin are found. 



These three groups are alone of practical importance. 



I. Albuminuria. Albumin never appears in normal 

 urine in appreciable quantity ; its presence must therefore 

 always be looked upon as an indication of disease. 



As a rule the albumin is secreted with the urine, in the 

 kidneys (renal albuminuria), in rare cases its presence is 

 due to admixture of blood or pathological products (acci- 

 dental albuminuria). 



The fact that healthy urine contains no albumin in ap- 

 preciable amount is explained by the impermeability of the 

 renal epithelium to albumin and by the limited normal blood 

 pressure. A change from the normal, such as may be 

 brought about by pathological conditions of the blood or in- 

 creased bodily temperature, may cause the appearance of 

 albumin in the urine. 



Hence, renal albuminuria can occur : 



1. As a result of changes in the renal tis- 

 sues due to inflammatory or degeneration processes ; here 

 we find not only albumin present, but the quantity of urine 

 may be increased by the addition of albuminous exudate. 



2. In lowering of arterial pressure; the 

 lower the pressure the easier can a diffusion of albuminous 

 substances take place. Pressure is lowered in weak heart or 

 in venous congestion (organic heart disease, emphysema). 

 Both conditions, after existing for some time, in addition 

 produce changes in the renal epithelium. 



3. In fever albuminuria is always present. Several 

 factors are active here. The lowered pressure may alone 

 account for it; the elevated temperature facilitates the pro- 

 cess ; continued fever produces changes in the renal epithe- 

 lium. In case of severe infectious fevers a direct injury to 

 the renal parenchyma probably occurs because in such cases 

 the urine is very rich in albumin. 



