PHYSIO LOG y. 



results with the aid of the microscope. The iodine gives a 

 yellowish-brown color to the protoplasm, and it can be more 

 distinctly seen. The nucleus is also much more prominent 

 since it colors deeply, and we can perceive within the nucleus 

 one small rounded body, sometimes more, the nucleolus. The 

 iodine here kills and stains the protoplasm. The proto- 

 plasm, however, in a living condition will resist for a time some 



other reagents, 

 as we shall see 

 if we attempt 

 to stain it with 

 a one per cent 

 aqueous solu- 

 tion of a dye 

 known as eosin. 

 Let us mount a 

 few living 

 threads in such 

 a solution of 

 eosin, and after 

 Fig. 2. Fig. 3. a time wash off 



Cell of spirogyra before treat- Cell of spirogyra after treatment ^^ -tain TVip> 

 ment with iodine. with alcohol and iodine. stain. 



protoplasm remains uncolored. Now let us place these threads 

 for a short time, two or three minutes, in strong alcohol, which 

 kills the protoplasm. Then mount them in the eosin solution. 

 The protoplasm now takes the eosin stain. After the proto- 

 plasm has been killed we note that the nucleus is no longer 

 elliptical or angular in outline, but is rounded. The strands of 

 protoplasm are no longer in tension as they were when alive. 



10. Let us now take some fresh living threads and mount 

 them in water. Place a small drop of dilute glycerine on the 

 slip at one side of the cover glass, and with a bit of filter paper 

 at the other side draw out the water. The glycerine will flow 

 under the cover glass and come in contact with the spirogyra 

 threads. f Glycerine absorbs water promptly. Being in contact 

 with the threads it draws water out of the cell cavity, thus caus- 



