PROTOPLASM 3 



(a) A SUPPLY OF MATERIAL from which it can be formed. 



(b) A SUPPLY OF ENERGY to bring about the construction. 



(a) The chemical elements in protoplasm are carbon, hydro- 

 gen, oxygen, nitrogen, sulphur, and phosphorus. These elements 

 are contained in the ingredients of the solution used. If yeast 

 be sown in distilled water, even if it be kept at a temperature 

 of 36 C. , it does not grow. 



(b) The energy is got by the breaking down of the sugar, 

 C 6 H 12 6 , into alcohol, C 2 H 6 0, and carbon dioxide, C0 2 . Such a 

 breaking down of a complex into simpler molecules liberates 

 energy, as is well seen when nitro-glycerine explodes, breaking 

 into carbon dioxide, water, oxygen, and nitrogen 



The energy can be used for the performance of work of any 

 kind, as, for example, the work of building up a fresh quantity 

 of the yeast plant out of the substances contained in the 

 solution. The history of the yeast plant shows that protoplasm, 

 when placed in suitable conditions, has the power of breaking down 

 certain complex substances, and of utilising the energy liberated 

 for building itself up. It is this power which has enabled 

 living matter to exist and to extend over the earth. 



How does protoplasm liberate the potential energy of such 

 substances ? 



The answer to this question has been given by the demon- 

 stration by Buchner that the expressed juice of the yeast torulae 

 acts on the sugar in the same way as the 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. These 

 enzymes all act by hastening reactions which go on slowly 

 without their presence, but they do not themselves take any 

 direct part in the reaction. Hence a very small quantity may 

 bring about an extensive change in the substance acted upon. 

 For the manifestation of their activity they 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 



