80 A TEXTBOOK OF PHYSIOLOGY 



haemoglobin are found increased by the new formation of corpuscles 

 in the red marrow. In rabbits taken from Basle (740 millimetres 

 barometric pressure) to St. Moritz (620 millimetres) the total haemo- 

 globin increased 12 per cent, and the blood- volume decreased 11 per 

 cent. The increase in the percentage of haemoglobin was 12 per cent. 

 Thus the body compensated for the attenuation of the air and lowered 

 partial pressure of oxygen. 



Cooling or bandaging a limb concentrates the blood therein. The 

 breathing of an excess of C0 2 and the taking of amyl nitrite dilutes, 

 of chloral hydrate concentrates, the blood. 



The Osmotic Pressure. The osmotic pressure of the whole blood 

 is measured by the depression of the freezing-point. Generally 

 A = 0-56 C. for human blood, but varies from -0-51 C. to 

 0-62 C. with the diet and amount of fluid ingested. If the 

 products of metabolism increase in the blood, owing to the fact 

 that they are not properly eliminated by the kidneys, A may be 

 increased According to some observers, if ^ constantly equals or 

 exceeds 0-58 C. it is a sign that both kidneys are diseased. 



The Electrical Conductivity of the Blood. As the blood-plasma 

 contains inorganic salts (electrolytes) in solution, it has the property 

 of conducting an electric current. Defibrinated blood is generally 

 employed for this measurement. The conductivity varies with the 

 relative proportion of corpuscles and serum being low with many 

 corpuscles and less serum, high with relatively few corpuscles and 

 much serum. In cases of anaemia the conductivity is greatly increased. 

 The corpuscles, owing to their colloid nature, lessen the conductivity. 



Viscosity. Blood compared to water is relatively a viscous fluid. 

 Its viscosity may be determined by allowing blood to flow under a 

 definite pressure through a capillary tube of known dimensions, and 

 measuring the outflow in a given time Taking the viscosity of water 

 as 1, that of the blood of man is 5-1 ; that of dog, 4-7 ; that of the cat, 4-2. 

 Viscosity generally varies in the same direction as the specific gravity. 

 Sweating increases it; increased temperature, on the other hand, 

 diminishes it. 



In the condition known as polycythaemia the viscosity may 

 become 9 or 10 times that of water. In this condition the red blood- 

 corpuscles are greatly increased in number in proportion to the plasma, 

 reaching as many as 11,000,000 per c. mm. On the other hand, in the 

 form of anaemia known as chlorosis or " greensickness," because of the 

 greenish look of the patient, the plasma is greatly increased in amount, 

 so that the corpuscles are relatively diminished, and the viscosity of 

 the blood is also much diminished, often to just over 2. The flow of 

 the blood is so controlled by the vaso -motor system that slight altera- 

 tions in viscosity are of little if any account. 



Analysis. The most accurate analyses of the blood have been 

 done upon that of animals ; the following table shows the quantitative 

 composition of the blood in the ox, horse, and man : 



