[58 ProciCdinys of llic Ohio State /Icadcmy of Science 



erased in strength to throw the blood into the aorta to keep 

 up the pressure necessary for the distribution of the blood 

 to the surface or to points of least resistance, which has a 

 tendency to equalize the temperature by the loss of heat. The 

 increased activity of the heart tends to increase the strength 

 of the muscle fiber of the heart itself the same as the strength 

 of any muscle is increased by exercise. Many failures of the 

 heart to act in emergencies are accoimted for from this lack 

 of exercise. People of sedentary ha])its are more subject tn 

 weak hearts. A cjuick run for a train or any temporary sud- 

 den call for heart force is not responded to for the very reason 

 that the heart has not been regularly exercised for strength 

 to meet more than the regular calls of the organism. Re- 

 sult : — Sudden death ; Cause : — heart failure. The arteries 

 like the heart are called upon under like circumstances to 

 stand a greater strain on account of the more forcible heart 

 beat. They are made up of muscular tissue as well as elastic 

 tissue. Unless they have been exercised properly they may 

 give way or lose their elasticity from the great stretching on 

 account of the weakness of the muscles. 



Another element in the circulation oi the blood and the 

 body fluids in general is the suction force caused by the res- 

 piratory movements. These are all brought about by the 

 activity of the muscles of the chest and the diaphragm. As 

 the muscles e(;n:raet, th.e chest cavity expands thereby reduc- 

 ing the pressure in the cavity. Since the blood is flowing to- 

 ward the cavity in the veins, the lack of the pressure here will 

 accelerate the blood in that direction. It will have a tendency 

 also to pull the lymph in the same direction and to increase 

 the flow of the lymph in the thoracic duet and the other lym- 

 jdiatic ducts that open into the veins which empty directly 

 into the heart. The lymphatic vessels all have valves opening 

 (inlv toward the jieart. so any movement of the lymph from 

 anv cause must be in that direction. We have already noticed 

 that the Ivmph collects nearly all of the impurities and carries 

 them to the veins near the heart. The increase in the per- 



