THE FLUIDS OF THE BODY 57 



out. If germs pass through these first stations into the lymph- 

 vessels beyond them, abscesses are formed in other situations. 

 A condition of " blood-poisoning," so called, is set up. 



The readiness with which leucocytes sacrifice themselves in 

 their efforts to remove germs and decaying tissue is a matter 

 of almost e very-day experience. The fatty matter produced 

 in the sebaceous glands of the skin normally overflows on to 

 the surface. It serves to render the skin supple and imper- 

 vious to water. Germs get into one of the sebaceous glands 

 of the face or of the eyelid. The contents of the gland begin 

 to decompose. Leucocytes enter it for the purpose of re- 

 moving the putrescent substance. They lose their vitality 

 and turn into pus corpuscles. The pimple or the stye bursts, 

 and pus and fatty matter are discharged together. 



That the conversion of leucocytes into pus cells is due to 

 want of oxygen has been shown by the following experiment : 

 A minute piece of phosphorus is placed beneath the skin. 

 Leucocytes gather round the spot with a view to removing the 

 tissue which the phosphorus has destroyed. But phosphorus 

 has so strong an affinity for oxygen that it exhausts the supply 

 in the area of tissue which surrounds it. The leucocytes die 

 before reaching the tissue immediately adjacent to the piece 

 of phosphorus. Their dead bodies form round it a raised ring 

 of pus cells. We can explain this readiness of leucocytes to 

 sacrifice themselves in their efforts to reach foreign matter 

 which needs to be removed, only by saying that the attraction 

 of the food is greater than the repulsion of lymph destitute 

 of oxygen. An amoeba placed in comparable circumstances 

 gives up the quest of food, however strongly chemiotaxic, and 

 retreats towards water which contains oxygen sufficient to 

 provide for its respiratory needs. 



Blood. A portion of the body fluid is enclosed within vessels 

 and kept in circulation by the heart. The heart pumps blood 

 into the aorta. This trunk gives off large arteries, which in 

 turn divide until the finest capillary vessels are reached. The 

 capillary tubes reunite to form veins, which, with the excep- 

 tion of those which collect food from the digestive organs, 

 convey the blood right back to the heart. The veins which 

 drain the stomach and intestines (the organs in which food is 

 prepared for absorption) and the spleen (the organ in which 



