300 PHYSIOLOGY OF NUTRITION. 



order to remove any traces of sulphuretted Hydrogen and hydro- 

 carbons which may be present. A small quantity of water must 

 be left above the mercury in the tubes of the retorts in order to 

 prevent the research material from being exposed to the vapour of 

 the mercury. The wheat grains lying in atmospheric air quickly 

 germinate ; those in Hydrogen do not germinate. Control experi- 

 ments, however, show that the grains exposed to the Hydrogen by 

 no means rapidly perish, but remain capable of germination for a 

 fairly long time (for several days at least), and if they are sub- 

 sequently exposed to conditions favourable to germination, in 

 presence of air, their embryos will develop. When the material 

 under investigation has been exposed to atmospheric air and 

 Hydrogen respectively for two or three days, it is removed from 

 the vessels, crushed in the mortar, and the pulp is treated with 

 20 c.c. of water. After some time we filter through filter paper 

 not previously moistened. If we now mix 10 c.c. of the filtrate 

 with 20 c.c. of dilute starch paste, the Iodine reaction shows that 

 the extract from the seedlings developed in the vessel containing 

 air acts energetically on the starch, while the extract from the 

 material kept in Hydrogen exhibits only a very slight power of 

 transforming starch. It is not greater than that of an extract 

 prepared by treating twenty dormant wheat grains, after pound- 

 ing in a mortar, with 20 c.c. of water. The experiment teaches, 

 therefore, that diastase can only be formed in the cells of higher 

 plants in presence of free atmospheric Oxygen. 1 



1 See Detmer, Botan. Zeitung, 1883, No. 37, and Pflaiizenphysiologisclie 

 U ntersuehunyen iiber Fermentbildung und fermentative Processe, Jena, 1884. 



115. The Estimation and Microchemical Detection of Glucose. 



Dextrose, maltose, etc., are capable of directly reducing 

 Fehling's solution. The sugars which behave in this manner are 

 grouped together under the general name of "glucoses.'' If it is 

 desired to estimate the amount of glucose in a sample of malt, 

 we first grind the material to powder in a hand-mill, and determine 

 the weight of dry substance in a small quantity of the powder. A 

 further quantity of the powder, say 3 gr., is now treated re- 

 peatedly with cold water, and the resulting solution is filtered. 

 Extracts prepared from seeds or seedlings, with which also we are 

 here concerned, frequently do not at once give a clear filtrate. 



