192 INTRODUCTION TO GENERAL PHYSIOLOGY 



sulphate. If a dilute solution in water be acted on by emulsin, 

 glucose and ethyl-alcohol are formed. 



Enzymes Act at their Surfaces. Take a quantity of ground 

 Soy beans containing urease. Add 75 per cent, alcohol, shake 

 together, and filter off a part. Add a few crystals of urea to this 

 filtrate and also to the suspension of the powder in alcohol. Keep 

 in a warm place for a day, and test for the production of ammonia 

 by aeration as described above (p. 182). A mere trace will be found 

 in the sample in which the filtered extract was used, arising from 

 the slight spontaneous change of urea. In that in which the solid 

 was suspended a large amount will be found. Thus urease acts 

 in a liquid in which it is insoluble. 



Catalytic Action. Faraday's platinum effect maybe obtained in 

 a modified way thus : Take a little spiral of fine platinum wire. If 

 held in forceps over the tip of a Bunsen burner and the gas turned on, 

 it is probable that no effect will be obtained owing to the surface 

 not being clean. Light the gas and allow the platinum to be heated 

 to a red heat, then put out the flame by pinching the tube, and as 

 soon as the wire has ceased to glow let the gas on again. The 

 platinum will gradually get red and the gas be ignited. If allowed 

 to become quite cold again it rapidly loses its activity. 



The oxidation of methyl alcohol by platinum may be seen 

 thus: Place a few c.c. of methyl alcohol in the test-tube of 

 Fig. 12 and in the horizontal part of the exit tube, which should be 

 fairly wide, some platinised asbestos, that is, asbestos coated with 

 finely-divided platinum. The bottle, empty, should preferably be 

 immersed in ice, but cold water will serve. Immerse the test-tube 

 in warm water and draw air through it over the platinum. The 

 reaction will probably not commence until the latter is warmed, but 

 will then continue of itself when the external heat is removed. If 

 the reaction has not been too violent, formaldehyde may be detected 

 by its smell in the condensing bottle. 



Add a few c.c. of methyl acetate to water as in the experi- 

 ment on p. 189. Add paste of castor-oil seeds with dilute acid, 

 and make just alkaline to phenol-phthalein. The red colour will 

 disappear much more rapidly than it did in the former experiment. 

 When this has taken place, make red again and observe the 

 renewed disappearance, and so on. The lipase acts as a catalyst 

 in accelerating the hydrolysis of the ester. 



Model. Some instructive experiments can be made with a 

 schema. Take a piece of polished plate glass about 3 ft. long and 

 6 in. broad, such as is sold for shelves in shops. Raise one end 

 on an adjustable support some 5 in. high. Carefully polish with 

 chamois leather so as to remove dust. Polish also the bottom of a 

 brass kilogram weight. Place the weight at the top of the sloping 



