PRACTICAL STUDY OF PROTOPLASM. 43 



experiment with another iu which a carmine solution e.g., 

 Beale's carmine or borax-carmine is used. Notice especially in 

 the latter case the failure of the cells to stain until they are 

 killed. How do you determine when the cells are dying and 

 when they are killed ? 



7. Repeat (5) and (6), using ciliated cells scraped from the 

 hinder part of a frog's mouth or from the oesophagus. 



8. Lay open the oesophagus of a frog (or better, of a turtle) 

 from the lower side, and pin it out flat with the inner surface ex- 

 posed. Place bits of moistened cork on the surface at the ante- 

 rior end. They immediately begin to travel backward along the 

 oesophagus, being propelled by the cilia. Incline the animal, and 

 note that the pieces of cork may be carried up a steep slope. 



9. To some fresh, healthy yeast from an actively fermenting 

 fluid add, under the cover-glass, an aqueous solution of eosine, 

 magenta, or aniline blue. Notice that very few cells are imme- 

 diately colored. Repeat the experiment, using yeast which has 

 been boiled for a moment. Report the result to the demon- 

 strator. Compare these experiments with a similar series in 

 which the ordinary iodine solution is used instead of eosine, etc., 

 and explain the difference in effect in the two cases. 



B. Proteids. 



1. Examine the " white" of an egg and cut it up with scissors. 

 Add its own bulk of water, and filter. Put some of the filtrate 

 into several small test-tubes, setting aside the rest for E. 2, and 

 apply the following tests for proteids : 



Tube No. 1. Add a few drops of strong nitric acid (HNO 3 ). 



A dense white or yellowish precipitate is formed. Boil for a 



moment, cool, and cautiously add ammonia (NH 4 OHV The 



" precipitate becomes of a bright orange color. (Xanthoproteic 



reaction.) 



Tube No. 2. Add a few drops of caustic soda solution, then 

 one or two drops of a solution of cupric sulphate, and heat. 

 Note the violet color. 



Tube No. 3. Heat in a water-bath, and note the coagulation. 



Tube No. -i. Heat as in (3), but more slowly, and determine 

 with a thermometer the coagulating point. Record the results 

 in everv case. 



