PROTOPLASM 



The behaviour of the yeast plant shows that such 

 protoplasm, when placed in suitable conditions, has the 

 power of by^eaking down certain complex substances, and of 

 utilising the energy so liberated for building itself up, and 

 thus increasing and growing. It is this power of using this 

 energy for growth which has enabled living matter to exist 

 and to extend over the earth. 



4. Liberation of Energy by Protoplasm. — How is this 

 oxidation and liberation of energy effected ? 



The answer to this question has been given by the 

 demonstration by Biichner that the expressed juice of the 

 yeast torulee acts on the sugar in the same way as the 



Fig. 1. — To show the relationship of the rate of enzyme action to tempera- 

 ture. The vertical lines represent different temperatures. The 

 dotted line represents the rate of enzyme action as modified by 

 temperature. The continuous line shows the destruction of the 

 enzyme as the temperature rises. The dash line shows the actual 

 rate of enzyme action as modified by these two factors. 



living yeast. The yeast therefore manufactures something 

 which splits the sugar. This something belongs to the 

 group of Enzymes or Zymins which play so important a 

 part in physiology generally. 



(1) Conditions of Enzyme Action. — For the manifestation 

 of their activity these enzymes require the presence of 

 water and a suitable temperature — in the case of the yeast 

 enzyme about 36° C. is the best. At lower temperatures 

 the reaction becomes slower and is finally stopped, and at 

 a higher temperature it is delayed and finally arrested by 

 the destruction of the enzyme (fig. 1). 



