430 A MANUAL OF PHYSIOLOGY 



drop or two of litmus solution, and, if necessary, enough of dilute 

 sodium hydroxide to just establish a blue colour. Then put the 

 test-tubes at 40 C., and examine after a time. No digestion will 

 have taken place in A, because the pancreatic juice, as secreted, does 

 not contain active trypsin. In B digestion may take place, because 

 the enterokinase in the intestinal mucous membrane will activate 

 the trypsinogen to trypsin. In C and D there will be evidence of the 

 production of reducing sugar and fatty acids respectively, since 

 the pancreatic juice, as secreted, contains active amylopsin and 

 steapsin. E will be unchanged unless by bacterial action. 



(/) Leucin and Tyrosin. As examples of amino-acids formed when 

 pancreatic digestion of proteins (fibrin or casein, e.g.] is allowed to 

 go on for some days,* leucin and tyrosin may be isolated. Add 

 bromine water by drops to 5 c.c. of the digest ; a pink colour indicates 

 tryptophane. If the ' digest ' be neutralized, then filtered, and the 

 filtrate concentrated and allowed to stand, a crop of tyrosin crystals 

 will separate out, since tyrosin is only slightly soluble in watery 

 solutions of neutral salts. These crystals having been filtered off, 

 the proteoses (albumoses) and peptones can be precipitated together 

 by alcohol, and afterwards separated, if that is desired, by redis- 

 solving the precipitate in water and throwing down the proteoses 

 by saturation with ammonium sulphate. The alcoholic filtrate will 

 contain any leucin that may be present, since that body is mode- 

 rately soluble in alcohol, as well as traces of tyrosin, which, however, 

 is much less soluble in this medium. On concentration, crystals of 

 both substances will be obtained. Tyrosin crystallizes characteristi- 

 cally from animal liquids in beautiful silky needles united into 

 sheaves, leucin in the form of indistinct fatty-looking balls, often 

 marked with radial striae and coloured with pigment (Figs. 169 and 

 170, p. 452). 



7. Bile. (a) Test the reaction of ox bile. It is alkaline to litmus. 



(b) Add dilute acetic acid. A precipitate of bile-mucin (really 

 nucleo-albumin) falls down. Some of the bile-pigment is also pre- 

 cipitated. Filter. (Pig's bile contains more of the mucin-like 

 substance than ox bile.) 



(c) Put a little of the filtrate from (b) or of the original bile into a 

 porcelain capsule, add a drop or two of a dilute solution of cane- 

 sugar, and mix with the bile. Then add a few drops of strong sul- 

 phuric acid, and stir. Then a few drops more of the sulphuric acid, 

 stirring all the time. A purple colour appearing at once, or after 

 gentle heating, shows the presence of bile-acids (Pettenkofer's reac- 

 tion). The bile may be diluted before the addition of the sulphuric 

 acid. In this case a greater amount of the acid must be added. 

 Examine the purple liquid in a test-tube with a spectroscope (p. 65). 

 Dilute the liquid with water, adding some sulphuric acid to partially 

 clear up the precipitate caused by the water. Two absorption bands 

 are seen, one to the red side of D, and the other, a stronger and 

 broader band, over and to the right of E. When only a very small 

 amount of bile-salts is present, the reaction is made more sensitive if a 

 solution of furfuraldehyde (i to 1,000) is used instead of cane-sugar. 



(d) Hay's Sulphur Test. Sprinkle a little sulphur (in the form of 

 the fine powder known as flowers of sulphur) on the surface of some 

 bile in a small beaker or deep watch-glass. The sulphur will soon 

 sink to the bottom. Repeat with water ; the sulphur will float. The 

 reaction is due to the diminution of the surface tension produced by 



* A little chloroform is added to prevent bacterial growth. 



