422 A MANUAL OF PHYSIOLOGY 



PRACTICAL EXERCISES ON CHAPTERS IV. AND V. 



Quantitative Estimation of Ferment Action. For pepsin an easy 

 method, although not a very accurate one, of estimating the rate at 

 which the fibrin disappears is to use fibrin stained with carmine. As 

 solution goes on, the dye colours the liquid more and more deeply, 

 and by comparing the depth of colour at any time with standard 

 solutions of carmine, we get the quantity of dye set free, and there- 

 fore of fibrin digested. This method cannot be used for trypsin. A 

 much better method is that of Mett (p. 318). Fluid egg-white is 

 sucked up into fine glass tubes (of i to 2 mm. bore). The tubes are 

 then heated in a bath at 95 C. For use short pieces (i or 2 cm. 

 long) are cut off and placed in i or 2 c.c. of the liquid to be tested, 

 the whole being kept at 38 to 40 C. At the end of a certain time 

 the length of the column of undissolved protein is measured with a 

 scale and low-power microscope. Deducting this from the length of 

 the tube, we get the length of the column digested. As a test of the 

 activity of a diastatic ferment, we take the amount of sugar formed 

 in a given time in a given quantity of a standard starch solution. 

 Where rapid work is required, glass tubes filled with tinted starch 

 paste may be used in the same way as the Mett's tubes. A more 

 accurate method, and yet a rapid and convenient one, is based upon 

 the time which is necessary in order that the iodine reaction with 

 starch may just disappear when a standard starch solution is digested 

 with a dilution of the ferment solution at 40 C. To determine 

 the activity of pancreatic juice as regards fat-splitting ferment, 

 the acidity of the emulsion formed by the juice and fat after standing 

 for a definite time at a given temperature (with occasional shaking) 

 can be estimated by titration with baryta solution. 



i. Saliva. Collection and Microscopic Examination of Saliva. 

 Chew a piece of paraffin-wax, or inhale ether or the vapour of strong 

 acetic acid. The flow of saliva is increased. Collect it in a porcelain 

 capsule. Examine a drop under the microscope. It may contain a 

 few flat epithelial scales from the mouth and a few round granular 

 bodies, the salivary corpuscles, the granules in which often show a 

 lively, dancing movement (Brownian motion). Filter the saliva to 

 free it from air-bubbles, and perform the following experiments : 



(a) Test the reaction with litmus paper. It is usually alkaline. 

 An acid reaction may indicate that bacterial processes are abnormally 

 active in the mouth. 



(b) Add dilute acetic acid. A precipitate indicates the presence 

 of mucin (p. 319). Filter. 



(c) Add a drop or two of silver nitrate solution to the filtrate from 

 (b). A precipitate insoluble in nitric acid, soluble in ammonia, 

 proves that chlorides are present. 



(d) Add to another portion a few drops of dilute ferric chloride 

 slightly acidulated with dilute hydrochloric acid, and the. same 

 quantity to as much distilled water in a control test-tube. A 

 reddish coloration is obtained, due to the presence of sulphocyanic 

 acid, which is combined with potassium and other bases in the saliva. 

 The colour is discharged by mercuric chloride. Or, a drop of saliva 

 may be allowed to fall from the mouth on a test-paper (prepared by 

 soaking filter-paper with a dilute starch solution, containing a little 

 iodic acid, and allowing it to dry in the air) . The paper is coloured 



