METABOLIC PROCESSES IN THE PLAXT. 290 



however, to be emphasised that only large proportions of acid 

 annul the action of diastase. If, on the one hand, we treat 25 

 c.c. of paste with 5 c.c. of malt extract, and, on the other hand, 

 25 c.c. of paste with 5 c.c. of malt extract and 2-3 mg. of 

 Citric acid, the transformation of the starch takes place more 

 rapidly in the latter fluid than in the former. Small quantities 

 of Citric acid, therefore (and small quantities of other acids 

 behave in a similar manner), do not arrest the action of diastase, 

 but on the contrary favour it. 



If, on the one hand, we mix 25 c.c. of starch paste at a tempera- 

 ture of 15 or 20 C. with 5 c.c. of malt extract at a temperature 

 of 15 or 20 C. and keep the temperature of the mixture at 15 

 or 20 C., and if, on the other hand, we mix together 25 c.c. 

 of paste and 5 c.c. of malt extract after cooling to 4 C., we can 

 readily satisfy ourselves by means of the Iodine reaction, that the 

 transformation of the starch by the diastase proceeds far more 

 rapidly at the higher than at the lower temperature. The 

 optimum temperature for diastatic action lies at 63 C. (Kjel- 

 dahl). 



If we heat malt extract to the boiling point, and mix the fluid, 

 after it has been allowed to cool, with paste, it is found that no 

 transformation of the starch ensues. The ferment has been de- 

 stroyed by the heat. 1 



1 See Detmer, Pflanzenplnjsiologische Untersuchungen tiber Fermentbildunf/ 

 iind fermentative Processe, Jena, 1884 ; also LandwirthschaftL JahrMcher, Bd. 

 10. 



114. The Production of Diastase in the Cells of Higher Plants. 



Into each of two retort-like vessels of about 90 c.c. capacity, we 

 introduce twenty air-dry wheat grains, fill the vessels with water 

 which has been boiled and then allowed to cool again, close the 

 mouths of the vessels with the finger, and invert each of them in 

 the manner indicated in Fig. 11, p. 34, in a beaker containing 

 mercury and water. At the end of twenty-four hours the water 

 in one of the vessels is replaced by atmospheric air, that in the 

 other by Hydrogen. We prepare the Hydrogen by the action of 

 arsenic-free Zinc on dilute Hydrochloric acid in a suitable ap- 

 paratus, and we pass the gas first through a solution of ca/ustic 

 potash, then through a solution of Potassium permanganate in 



