2536 Journal of Applied Microscopy 



GENERAL PHYSIOLOGY. 



RAYMOND PEARL, University of Michigan. 



Books and Papers for Review should be Sent to Raymond Pearl, Zoological Laboratory, 

 University of Michigan, Ann Arbor, Mich. 



Clowes, G. H. A. The Relationship between In this experimental study of the urine 

 Uie Freezing Point Depression and Specific ^f normal and pathological subjects, 

 Gravity of Urine, under \ arying Conditions a o 



of Metabolism, and its Clinical Value in the carried on by the methods of physical 

 Estimation of Sugar and Albumin. Amer. chemistry, the author has deduced some 

 Jour. Physiol. 9: 319-343, 1903. 



valuable constants for practical work 



in urine analysis. He finds in agreement with earlier workers that in normal 

 urine the depression of the freezing point is directly proportional to the specific 

 gravity, and may be determined from the latter by multiplying the figures after 

 the decimal point by 75. (As an example, if the specific gravity is 1.022, 0.022 

 X 75 = 1.65, which is found by experiment to be the depression of the freez- 

 ing point of such a solution in degrees C.) In pathological urines other than 

 those containing sugar and albumin, the same tendency to maintain a constant 

 proportion between the freezing point and specific gravity may be observed, 

 although within rather wider limits than in the case of normal urine. The aver- 

 age weight of the molecule or ion in urine may be determined from these figures 

 as approximately 5() to 60, making use of Beckmann's formula, M ^ E '" , where 

 M^ molecular weight of the substance dissolved ; E :^ a. constant having the 

 value of 18.5 when water is employed as the solvent ; m ^^ the quantity of sub- 

 stance dissolved, assumed in this case to be 2.3o grams of substance for each 

 0.01 of specific gravity; and ^ ^ the observed depression of the freezing point 

 (0.75° for each 0.01 of specific gravity). In diabetic urines, the quantity of 

 sugar may be very readily estimated by determining the lowering of the freezing 

 point of the urine in question, and calculating the theoretical lowering of the 

 freezing point from the specific gravity. The difference between these two 

 quantities in degrees C, when multiplied by 6, gives a very close approximation 

 of the actual percentage of sugar present in the solution. This factor, 6, calcu- 

 lated on a theoretical basis and subsequently confirmed in practice, is dependent 

 on the fact that the molecular weight of sugar is ISO, whilst the average of urine 

 solids is below 60. The quantity of albumin may be estimated by determining 

 the specific gravity and freezing point in a urine to which a couple of drops of 

 dilute acetic acid has been added, then boiling in order to precipitate the albu- 

 min, filtering and once more determining the specific gravity and freezing point. 

 The second specific gravity is reduced to the same ionic concentration as the 

 first, by multiplying its decimal portion by the freezing point before boiling, and 

 dividing by the freezing point obtained after boiling. This calculated specific 

 gravity is then substracted from the original specific gravity determined before 

 boiling, and the difference multiplied by the factor 400, which gives the percent- 

 age of albumin. In a urine containing both albumin and sugar the former is 



