544 



ILL USTRA TI VE EXPERIMENTS 



salicylic acid may be used (p. 562). It is necessary, of course, to maintain 

 the correct /jH for the particular enzyme. 



48. Demonstration of the Presence of a Lipase in an Extract. (Benger's 

 Liquor Pancreaticus.) 



Take 90 c.c. of distilled water, 10 c.c. of M/3 secondary sodium phosphate 

 and 20 drops of tributyrin, and shake together for 10 minutes. Filter, 

 rejecting the first few cubic centimetres of the filtrate. This gives a fine 

 suspension of fat in a buffered solution of about ;;H 8. To 50 c.c. of this 

 mixture at 38° C. add 2 c.c. of Benger's Liquor Pancreaticus. Mix and rapidly 

 withdraw about 5 c.c. for stalagmometric investigation (Experiment 17 (1) ). 

 The drop number so obtained is taken as that of a diluted tributyrin mixture. 

 If a pancreatic lipase is present in the liquid under test, it should cause the 

 splitting of the fat into butyric acid and glycerol, which mixture has a higher 

 surface tension than the parent substance, and so gives fewer drops per 

 3 c.c. The mixture is kept at about 38° C, and lots of 5 c.c. are removed, 

 cooled, and the drop number taken every 5-10 minutes, depending on the 

 activity of the lipase. 



Time (minutes) . 

 Drop No. 





 120 



5 

 120 



15 

 113 



25 

 109 



35 

 101 



49. Estimation of the Relative Lipolytic Activity of an Extract of 

 Pancreas. 



Prepare a series of test tubes with 2 c.c. of the following dilutions of 

 1/20 Benger's Liquor Pancreaticus : 1/1, 1/2, 1/4, 1/8, 1/16, 1/32. Place a 

 seventh tube about the middle of the series and put in it 2 c.c. of the extract 

 of pancreas. Now add as rapidly as possible to each tube in order 5 c.c. of the 

 phosphate-tributyrin mixture used in the previous experiment. Immerse 

 all the tubes in a water bath at 38° C. for 30 minutes. Cool. Estimate the 

 relative surface tension of the mixtures by the capillary rise method (Experi- 

 ment 17 (2)), starting at the right, i.e. with the greater dilutions of the 

 enzyme. Suppose the unknown fluid rose in the tube just a little less than 

 in tube 3 but a little more than in tube 4, then the pancreatic extract would 

 approximately be in strength between 1/4 X 1/20 = 1/80 and 1/160 of the 

 liquor pancreaticus. One may then proceed as in the experiment above to 

 define the strength more accurately. 



50. Chemical Gardens. 



(a) Place 50 c.c. of potassium ferrocyanide in a glass jar or beaker and 

 add a small particle of ferric chloride (small pea). A semipermeable mem- 

 brane of ferric ferrocyanide (Prussian blue) is formed round the solid. 

 Endosmosis occurs and peculiar growths may be formed, 



(6) Add a drop of almost saturated potassium ferrocyanide from the 

 end of a glass rod to a solution of copper sulphate (bench reagent). A 

 semipermeable membrane of copper ferrocyanide is formed round the drop 

 and endosmosis takes place. This causes an increase in the concentration 

 of the copper sulphate immediately round the drop and blue " rootlets " 

 may be seen descending from the drop. These are due to the increased 

 density of the sulphate (see also Experiment 5 {a) ). 



51. Leduc's Growths. 



A small flat-sided jar, e.g a specimen jar, is filled with a 1-2 per cent, 

 solution of gelatin to which is added just enough potassium ferrocyanide to 

 give it a pale green colour. Just before the gelatin has set, a little seed 



