i 17. I 'our out a thin layer f collodion -olution mi a mercury sur- 

 face in a petri di-h and allow it to harden -omewhat. \\'hile still flexi- 

 ble remove tin- lilni fnun the mercury >urface and tie tightly on the 

 end of a thi-tle tnhe. Prepare two of thc-c "osmometers". Fill 

 . iiu I \\ith in J -ugar-formol solution to a p int on the stem 

 me inch aho\e the hull). Fill the other ( /> ) with water to a point 

 \\nhin "lie inch of the top of the tuhe. Place i/ in water and /' in 

 m _ -ugar-formol -olution in a heaker. .Vote any change in the 

 level . >f the nieiii-cn- of ,; and /'. I low high doe- the level of sugar 

 in (/ become? Does it then remain stationary? Kxplain all the 

 plieii'-mena noted in connection with the experiment, leaving the 

 . Milometers -et up for -cveral day-. 



I |S. Prepare- two test-tnhe collodion hag- a- follows: The te-t- 

 tuhe mu-t he cleaned with alcohol and dried thoroughly. Pour 

 ollodion -olutioii into a dry clean test-tuhe and then pour it out 

 -lowly into the collodion hottle. revolving the test-tube so a- to coat 

 the gla-- evenly \\ith a thin film of collodion. Allow this to harden 

 -onieuhat. then gently pry off the edge and allow -oine water to 

 run down hetween the tilm and the te-t-tuhe. P.y carefully ]>rying 

 and pulling the film may he entirely -eparated from the glass. Fill 

 with water to make -ure there are no leaks. If the collodion hags 

 are pu-fcet till one (a) with m 4 salt solution, and tie with a 

 piece i if -tring ahont the middle 50 a- to ohtain a firm -alt water 

 tilled hag. Fill the other ( /> ) half full of alhumin solution and tie 

 off so a- to lea\e -onie air enclosed. Note that it is not firm. Then 

 place <; in Jm -all -olutioii ami /' in water. Xote any change- in 

 rigidity of the hag-? F.xplaiiation ? 



i i 1 ;. Place a drop of frog'- him id corpu-cles in water in a watch- 

 gla-s and examine <//nV/.-/v under the micro-cope. 



Place a drop of -n-pended frog'- lilood corpuscles in m XaCl solu- 

 tion and examine under micro-cope. 



What happen- in each case? Kxplain. Xote -imilarity to the 

 preceding experiment. 



i jo Osmotic prcssitri' in li-iii,/ c^lls. f'litsni<>lvsis. Place 

 >pirog\i-.i lilament- in cane--ngar -ohnion of concentrations: m J, 

 in i,. m 4. m 5. m '', m -. m S. and in I\X< >. -olution- of the -ame 

 .-..infiltration-, in \\atch-gla- X'ot,' carefully under the micro- 



pe am changi-- of volume of the prot.,pla-m within the cell 

 walls. What solution jn-t fail- to pla-mo]y-e in the ca-e of hoth 



[ar and l\ ' ' Take the avera-e of tin- filament- in the di-h. 

 .hat i- the o-niotic pr, x-,,re of the -ap of Spin.gyra cell- a- deter- 



