80 THE BODY AT WORK 



about once a minute. By their contraction the blood is 

 squeezed out of the sponge. 



If the spleen be enclosed in an air-tight box (an oncometer), 

 from which a tube leads to a pressure-gauge a drum covered 

 with thin membrane on which the end of a lever rests, or a 

 bent column of mercury on which it floats the pressure- 

 gauge shows the changes in volume of the spleen. The long 

 end of the lever, which records the variations of pressure in 

 the gauge, may be made to scratch a line on a soot-blackened 

 surface of travelling paper. A record of the variations in 

 volume of the organ, which can be studied at leisure, is thus 

 obtained. It shows that the spleen is sensitive to every change 

 of pressure in the splenic artery. Small notches on the tracing 

 correspond to the beats of the heart. Larger curves record 

 the changes of blood-pressure due to respiration. A long slow 

 rise and fall marks the rhythmic dilation and contraction of 

 the spleen itself. 



One of the three large arteries into which the coeliac axis 

 divides delivers blood to the spleen direct from the aorta. 

 The splenic vein joins the portal vein shortly before it enters 

 the liver. Thus the spleen is placed on a big vascular loop 

 which directs blood, not long after it has left the heart, from 

 the aorta, through the spleen, to the liver. 



The peculiar construction of the splenic pulp which brings 

 the blood more or less to rest within its sponge-work, and the 

 transmission to the liver of the blood which leaves the spleen, 

 indicate that it is an organ in which blood itself receives 

 some kind of treatment. It is not passed through it, as it is 

 through all other parts of the body, in closed pipes. The 

 spleen is a reservoir, or a filter - bed, into which blood is 

 received. 



The red blood-corpuscles of mammals are cells without 

 nuclei, and with little, if any, body-protoplasm. They are 

 merely vehicles for carrying haemoglobin. We should deny to 

 them the status of cell, if it were possible to prescribe the 

 limit at which a structural unit ceases to be entitled to rank 

 as a cell. They are helpless creatures, incapable of renewing 

 their substance or of making good any of the damage to which 

 the vicissitudes of their ceaseless circulation render them 

 peculiarly liable. It is impossible to say with any approach 



