IO6 PRACTICAL PHYSIOLOGY. [XVI. 



urinometer in it. Bring the vessel to the level of the eye, and as 

 soon as the instrument comes to rest, read off the mark on its 

 stem opposite the lower surface of the meniscus against a bright 

 back-ground. 



Precautions. i. The vessel must be so wide that the urinometer can float 

 freely and not touch the sides. 2. The instrument must be dry before being 

 placed in the fluid. 3. The urine itself must be clear and free from air- 

 bubbles on the surface ; the latter can be readily removed by means of a fold 

 of blotting-paper. N.H. It is always necessary to take the specific gravity 

 of the "mixed" urine of twenty-four hours. 



Low S.G. Under normal conditions the s.g. varies inversely as the quantity 

 of urine passed. All causes which increase the water of the urine only, e.g., 

 drinking on an empty stomach ; after hysteria ; in diabetes insipid us or poly- 

 dipsia. N.B. If continually below 1015, suspect diabetes insipidus or chronic 

 Bright's disease. 



High S.G. When the urine is concentrated, diabetes melliins, due to a 

 large amount of grape sugar ; first stages of acute fevers ; rapid wasting of 

 the tissues, especially if associated with sweating or diarrhoea. It is highest 

 normally three to four hours after a meal ; and as it varies during the day, it 

 is necessary to mix the urine of the twenty- four hours, and test the specific 

 gravity of a sample of the "mixed urine." N.B. If above 1025 and the 

 urine be pale, suspect saccharine diabetes. 



5. Estimation of the Amount of Solids from the S.G. By 



Christ/son's formula (" Haser-Trapp's coefficient "), " multiply the 

 last two figures of a specific gravity expressed in four figures by 

 2.33. This gives the quantity of solid matter in every 1000 parts," 

 i.e., the number of grams in 1000 cc. (33^ oz.). 



Example. Suppose a patient to pass 1200 cc. of urine in twenty four hours, 

 and the sp. gr. to be 1022, then 



22 x 2. 33 = 5 1 . 26 grams in 1000 cc. 

 To ascertain the amount in 1200 cc. 



51.26 x 1200 

 1000 : 1200:: 51. 26: 3?= iooo~ =6r<51 g rams - 



This formula is purely empirical, and is not applicable where the variations 

 are very marked, as in saccharine diabetes and some cases of Bright's disease, 

 where there is a great diminution of urea. 



The normal quantity of solids, or the total solids sometimes 

 spoken of as "solid urine" is about 70 grams (2 oz.) in twenty- 

 four hours, i.e., 1000 to 1050 grains. Parkes gives an average 

 of 945 grains per day for an average adult male between twenty 

 and forty years of a,ge. The latter estimate gives about 20 grains 

 of solids per fluid ounce of urine, or about 4 per cent, of solids. 



6. Odour is " peculiar " and " characteristic," somewhat aromatic 

 in health. 



