52 A MANUAL OF PHYSIOLOGY 



sample. Thus, the specific gravity of a drop of blood having 

 been measured, a certain quantity of normal saline (a "5 to 

 7 per cent, solution of sodium chloride) may be injected 

 into a vein, and the specific gravity again determined. Or 

 the electrical resistance of a small sample of blood may 

 be measured before and after injection of a given quantity 

 of a substance, such as sodium chloride, which reduces it. 

 Or the total solids may be determined in a specimen before 

 and after injection of a known weight of distilled water. 

 Or an animal may be caused to inspire carbonic oxide 

 for a given time ; from the quantity taken in, and the 

 quantity fixed by a known weight of blood withdrawn from 

 the animal, the weight of the whole blood maybe calculated. 

 The quantity of blood in the body was greatly over- 

 estimated by the ancient physicians. Avicenna put it at 

 25 lb., and many loose statements are on record of as 

 much as 20 lb. being lost by a patient without causing 

 death. The proportion of blood to body-weight has been 

 found by accurate experiments to be in man and the dog 

 I : 13, new-born child I : 19, cat I : 14, horse I : 15, frog 

 i : 17, rabbit I : 19. Fig. n illustrates the distribution of 

 the blood in the various organs of a rabbit. The liver and 

 skeletal muscles each contain rather more than one-fourth ; 

 the heart, lungs, and great vessels rather less than one- 

 fourth ; and the rest of the body about one-fifth, of the total 

 blood. The kidney and spleen of the rabbit each contain 

 one-eighth of their own weight of blood, the liver between 

 one-third and one-fourth of its weight, the muscles only 

 one-twentieth of their weight. 



Lymph and Chyle. 



Lymph has been defined as blood without its red cor- 

 puscles (Johannes Muller) ; it is, in fact, a dilute blood- 

 plasma, containing leucocytes, some of which (lymphocytes) 

 are common to lymph and blood, others (coarsely granular 

 basophile cells) are absent from the blood. The reason of 

 this similarity appears when it is recognised that the plasma 

 of lymph is derived from the plasma of blood by a process 

 of physiological filtration (or secretion) through the walls of 



