34 A MANUAL OF PHYSIOLOGY 



Physical and Chemical Properties of the Blood. 



Fresh blood varies in colour, from scarlet in the arteries 

 to purple-red in the veins. It is a somewhat viscid liquid, 

 with a saline taste and a peculiar odour. Its reaction is 

 alkaline to litmus-paper, chiefly owing to the presence of 

 di-sodium phosphate (Na 2 HPO 4 ) and sodium carbonate. 

 The alkalinity is not constant ; it is increased during 

 digestion, when the acid of the gastric juice is being 

 formed ; it is lowest in the morning, and highest in the 

 afternoon. It is diminished by muscular exertion, owing 

 to the formation of lactic acid ; and since acid substances 

 seem to be produced in all active tissues, the alkalinity of 

 venous is less than that of arterial blood. In herbivorous 

 animals the alkalinity 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 change, the acid 

 being neutralized by ammonia, which is split off from the 

 proteids. In many diseases, however, and particularly in 

 those accompanied by fever, this protective mechanism 

 breaks down, the alkalinity of the blood becomes seriously 

 reduced, or even, as has sometimes been observed in diabetic 

 coma, gives place to an acid reaction. Chloroform appears 

 to cause a diminution in the alkalinity of the blood, and 

 acute alcoholic intoxication has a similar effect, owing to 

 the production of volatile fatty acids. It is possible that 

 the use of ammonia after a drinking bout for the bracing 

 effect attributed to it by experienced topers may be explained 

 by its power of neutralizing these acid products. The 

 average alkalinity of human blood, as estimated by titration 

 with a standard acid after the corpuscles have been broken 

 up, is that of a "4 per cent, solution of sodium hydrate 

 (Loewy). 



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 



