THE CIRCULATING LIQUIDS OF THE BODY 25 



dioxide and to preserve one of its essential properties an 

 almost neutral reaction in the presence of an excessive intake 

 or production of acid substances. In herbivorous animals the 

 carbon dioxide content of the blood is easily lessened by the 

 administration of acids, but in carnivora and in man it is much 

 more difficult to bring about such a decided effect, the acid 

 being neutralized by ammonia, which is split off from the pro- 

 teins. In many diseases, however, and particularly in those 

 accompanied by fever, this protective mechanism breaks down, 

 and the alkalinity of the blood, as measured by its content of 

 carbon dioxide, becomes seriously reduced. 



Specific Gravity of Blood. The average specific gravity of 

 blood is about 1066 at birth. It falls during infancy to about 

 1050 in the third year, then rises till puberty is reached to about 

 1058 in males (at the seventeenth year), and 1055 in females (at 

 the fourteenth year). It remains at this level during middle 

 life in males, but falls somewhat in females. In chlorotic 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 dissolved 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. For instance, in a case of 

 pernicious anaemia the conductivity of the blood was found to 

 be almost double that of normal human blood, while the con- 

 ductivity of the serum was normal. The most influential factor 

 which governs this variation is the relative volume of the cor- 

 puscles and serum. When the blood is relatively 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 corpuscle refuses passage to the ions 

 of the dissociated molecules, which, in virtue of their electrical 

 charges, render a liquid like blood a conductor (p. 400), 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 (Practical Exercises, p. 60). 



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

 determined in the writer's laboratory by Hammerschlag's method (p. 54) 

 was 1054-4. In 149 of these the variation was from 1050 to 1065 ; in 94 

 ( or 57 P er cent, of the whole), from 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. 



