OXIDATION IN THE TISSUES. 199 



hardly conceivable that oxidation similar to that occurring with- 

 in the body can take place in a solution of sodium chloride. 



RELATION OF OXIDATIVE PROCESS TO ACTIVITY. Under ordinary 

 conditions the blood has a supply of food and oxygen sufficient 

 for the needs of the body. An excess of either does not intensify 

 the oxidative process. An animal will give off the same amount 

 of carbon dioxide in an atmosphere of pure oxygen as it will 

 under ordinary conditions. This fact indicates that the oxida- 

 tive processes are governed not by the supply of food or oxygen, 

 but rather by the actual needs of the tissues. A muscle freshly 

 removed from the body may be made to contract, and will give 

 off carbon dioxide for some time in the entire absence of oxygen 

 in the surrounding medium. Another feature of this experiment 

 is that for a time after the muscle has ceased to contract, it will 

 produce heat and take up a large amount of oxygen. Indeed 

 the maximal intake of oxygen and output of heat often occurs 

 after the actual period of work. In this respect the muscle can 

 be likened to a storage battery which is charged by the actual 

 expenditure of energy and delivers quickly the energy stored 

 up when the circuit is closed. If the volume intake of oxygen 

 and output of carbon dioxide is measured, it will be found that 

 the amounts are greatly increased during periods of tissue activ- 

 ity. Experiments have demonstrated that a muscle at full work 

 will use up its own* volume of oxygen in ten minutes. To supply 

 such an amount of oxygen requires' a very high degree of effi- 

 ciency on the part of the distributing agent, the blood. 



PHYSICAL LAWS GOVERNING SOLUTION OF GASES. A brief re- 

 view of the physical laws governing the solution of gases in water 

 will help us materially to understand the mechanism of the trans- 

 portation of oxygen and carbon dioxide by the blood and the 

 respiratory mechanism in general. 



The solubility of a gas in a fluid is measured by the number of 

 cubic centimetres of gas which one cubic centimetre of fluid will 

 dissolve under standard conditions of temperature and pressure. 

 Such a figure is known as the coefficient of solubility. For ex- 

 ample, pure carbon dioxide gas under standard conditions of 

 temperature and pressure (760 mm. pressure and 15.5 degrees 



