268 EXPERIMENTAL PHYSIOLOGY 



of the potato is this most evident? To bits of potato in an atmo- 

 sphere of coal gas (free from oxygen) add (without admission of 

 oxygen) a few drops of guiacum. Should be no colour Why? 

 Now admit air. Result? 



5. Is digestion in protozoa comparable to that in man? Test 

 alizarin in acid and alkali to determine colour changes. Feed 

 paramecia with a suspension of alizarin. Shortly after ingestion 

 the globule of alizarin should indicate digestion in an acid medium. 

 In what region of the animal does this take place? Later in the 

 course of cyclosis, an alkaline medium may be shown. 



6. Write a statement concerning the characteristics of enzymes 

 brought out in these experiments. 



V. Buffer action and determination of PH. 

 Titrate N/10 NaOH against N/10 HC1. Do the same with 



i anS N/10 NaHCO 3 and N/10 Na 2 CO 3 . How do 



you account for the differences obtained? (Bayliss, Prin. Gen. 

 Phys., p. 203-205). 



Place on a slide small bits of ciliated epithelium from each of 

 three regions of a frog's mouth, anterior, middle, and posterior. 

 Find the concentration of acetic acid which will stop the movement 

 of the cilia in the anterior piece in three minutes. This can be 

 done by diluting one drop of a stock solution of acetic acid with a 

 definite number of drops of distilled water. Note the time when 

 the ciliary motion ceases in each of the other two pieces. Place 1 c.c. 

 of the solution of acetic acid which stops ciliary action in the 

 anterior piece in three minutes in a Pyrex narrow-bore tube, add 

 a few drops of an appropriate indicator (brom-phenol blue) and 

 match the resulting colour with the appropriate colour in the colour 

 chart of Clark's " Determination of Hydrogen-Ions", page 40. 

 This will give you the pH of the solution. 



Repeat using HC1 as the acid, and thymol blue as indicator. 



What is the relation of acids to ciliary movement? Is there any 

 difference in the effectiveness of organic and inorganic acids, or is 

 the hydrogen-ion concentration the only factor? . How do you 

 account for the fact that cilia from the more anterior regions are 

 more susceptible to the acid? 



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