PASTEUR EFFECT 



49 



An impressive physiological example of a mechanism utilizing 

 both respiratory and fermentative energy supply is the muscle. 

 Figures 1 and 2, after experiments by Bang (1), reproduce measure- 

 ments of oxygen consumption and lactic acid formation (blood 

 lactate) on human beings during physical work. During a prolonged 

 period of not too hard work (Figure 1) blood lactate at first increases 

 moderately but returns, during the first quarter of the period, almost 

 to the resting level. An anaerobic energy supply is observed only at 

 the beginning, when an adequate oxygen supply is lacking, and until 

 respiration climbs to the equilibrium level. For excessive short-term 

 work the picture is different, as shown in Figure 2. An excessive and 

 long-continued increase of blood lactate signifies a large expenditure 

 of anaerobic energy. In such a situation the adaptation is much too 



WORK 



BLOOD 



LACTIC ACID 



millimolcs per liter 



30 



2- 



I •• 



60 Minutes 



OXYGEN 

 liters per minute 



Figure 1. — Oxygen consumption and blood lactate with moderate work. The 

 slight initial rise of lactate output coincides with the period of adaptation, before 

 the oxygen consumption rises to the equilibriimi level. (After O. Bang, ref. 1.) 



