454 



DIGESTION AND ABSORPTION 



digested. This method cannot be used for trypsin. A much better 

 method is that of Mett (p. 343). 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. 



For amylolytic ferments 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. 



5. Saliva Collection 

 and Microscopic Examina- 

 tion of Saliva. Chew a 

 piece of paraffin-wax, or 

 inhale ether or the vapour 

 of strong acetic acid . The 

 flow of saliva is in creased. 

 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 sali- 

 vary corpuscles, the gran- 

 ules in which often show 

 a lively, dancing move- 

 ment (Brownian motion) . 

 Filter the saliva to free it 

 from air-bubbles, and per- 

 form the following ex- 

 periments : 



(a) Test the reaction 

 with litmus paper. It is 

 usually alkaline. An acid 

 reaction may indicate 

 that bacterial processes 

 are abnormally active in 



Fig. 173. Effect of Serum and Adrenalin on Con- 

 tractions of a Segment of Intestine. Rabbit's 

 intestine contracting in Ringer's solution. At 

 55 the Ringer's solution was replaced by dog's 

 serum, and this at 56 by adrenalin (1:5,000,000) 

 in serum. At 57 this weak adrenalin solution was 

 replaced by a stronger one (i: 500,000) in serum. 

 Time-trace, half-minutes. (Reduced to half.) 



the mouth. 



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

 mucin (p. 344). 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 arc 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 com- 

 bined with potassium and other bases in the saliva. The colour is dis- 

 charged 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 blue by the union of the 



