THE CIRCULATING LIQUIDS OF THE BODY 35 



anaemia of young women it may be as low as 1030 or 1035. 

 It rises in starvation. Sleep and regular exercise increase 

 it (Lloyd Jones).* The specific gravity of the serum or 

 plasma varies from 1026 to 1032. 



The Electrical Conductivity of Blood. The liquid portion of the 

 blood conducts the current entirely by means of the electrolytes dis- 

 solved in it, the most important of these being the inorganic salts ; 

 and the conductivity of the serum varies, in different specimens of 

 blood, within a comparatively narrow range. The conductivity of 

 entire (defibrinated) blood, on the contrary, varies within wide limits ; 

 and the most influential factor which governs this variation is the 

 number of the corpuscles suspended in it. When the blood is rela- 

 tively rich in corpuscles and poor in serum, its conductivity is low ; 

 when it is poor in corpuscles and rich in serum, its conductivity is 

 high. The explanation is that the envelope of the corpuscle refuses 

 passage to the dissociated molecules (the ions), which, in virtue of 

 their electrical charges, render a liquid like blood a conductor 

 (p. 362). or permits them only to pass very slowly, so that the intact 

 red corpuscles have an electrical conductivity so many times less 

 than that of serum, that they may, in comparison, be looked upon as 

 non-conductors. 



The Relative Volume of Corpuscles and Plasma in Unclotted 

 Blood, or, what can be converted into this by a small correction, 

 the relative volume of corpuscles and serum in defibrinated 

 blood, can be easily determined, with approximate accuracy, by 

 comparing the electrical conductivity of entire blood with that of its 

 serum. f Another simple method is to centrifugalize a small quantity 

 of blood, after mixing it with a known amount of a v\ per cent. 

 solution of potassium bichromate, in a glass tube of narrow bore 

 (haematocrite) until the corpuscles have been collected into a solid 

 * thread ' at the outer extremity of the tube. Their volume and that of 

 the clear liquid which has been separated from them are then read off 

 on an adjacent scale. By these and other methods too elaborate for 

 description here, it has been shown that the plasma or serum usually 

 makes up rather less than two-thirds, and the corpuscles rather more 

 than one-third, of the blood. But this proportion is, of course, liable 

 to the same variations as the number of corpuscles in a cubic milli- 

 metre of blood. It depends, further, the number of corpuscles being 



* In 165 students (male) the average specific gravity of the blood, as 

 determined by Hammerschlag's method (p. 57) was ic-54'4. In 149 of 

 these the variation was from 1050 to 1065 ; in 94 (or 57 per cent, of the 

 whole), frorfi 1054 to 1060 ; in 4, from 1046 to 1049 ; in 9, from 1066 to 

 1070. In 3 the specific gravity was only 1040 to 1042. 



f The formula p = -? (174 -X()), where p is the number of c.c. of 



AW 



serum in 100 c.c. of blood ; A(3), X(j), the conductivity respectively of 

 the blood and serum (both measured at or reduced to 5 C., and ex- 

 pressed in reciprocal ohms multiplied by io 8 ), may be used in the calcu- 

 lation. 



32 



