idi 



STUDIES IN PHYSIOLOGY 



and grape sugar solution) of different density (the liquid 

 within the thistle tube being the more dense), these liquids 

 separated by an animal membrane. 



On examining the apparatus after several hours, we find 

 that the solution within the thistle tube has risen several 

 inches, while the water in the bottle is at a lower level than it 

 was at first. It is evident that some of the water has passed 

 through the membrane of the intestine, and has mingled with 



the grape sugar solution. 

 Another fact becomes evi- 

 dent when we boil with 

 Fehling's solution a little 

 liquid in the bottle outside 

 the thistle tube. The 

 deep red color of the mix- 

 ture proves the presence 

 of grape sugar. Two cur- 

 rents, therefore, have been 

 passing through the ani- 

 mal membrane, but from 

 |P the level of the two liquids 

 we know that the amount 



of water that has gone into 

 FIG. 37. Apparatus to illustrate the ., . , . ., . , 



Principles of Osmosis. the thistle tube is greater 



than the amount of grape 



sugar solution that has passed out. If the apparatus is 

 allowed to stand for several days, the liquid within the tube 

 may rise to a height of several feet. From the preceding 

 observations we derive the following 



Law of Osmosis. When two liquids of different density are 

 separated by an animal (or plant} membrane, they tend to 

 mingle, and the greater Jloiv is always from the less dense to the 

 more dense. 



Two other pieces of apparatus similar to that already 

 described should be prepared, the second thistle tube being 

 filled with a rather thin starch paste, and the third with 



THISTLE TUBE THISTLE TUBE 



No. 1 No. 2 



THISTLE TUBE 

 NO. 3 



