FREE BOOKS

Author's List




PREV.   NEXT  
|<   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77  
78   79   80   81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   >>   >|  
place in part according to a general principle, known as _osmosis_, or dialysis. [Fig. 31] Fig. 31--*Vessel* with an upright membranous partition for illustrating osmosis. *Osmosis.*--The term "osmosis" is used to designate the passage of liquids through some partition which separates them. Thus, if a vessel with an upright membranous partition be filled on the one side with pure water and on the other with water containing salt, an exchange of materials will take place through the membrane until the same proportion of salt exists on the two sides (Fig. 31). The cause of osmosis is the motion of the molecules, or minute particles, that make up the liquid substance. If the partition were not present, this motion would simply cause a mixing of the liquids. *Conditions under which Osmosis occurs.*--Osmosis may be shown by suitable experiments (see Practical Work) to take place under the following conditions: 1. The liquids on the two sides of the partition must be _unlike_ either in density or in composition. Since the effect of the movement is to reduce the liquids to the same condition, _a difference in density causes the flow to be greater from the less dense toward the denser liquid_, than in the opposite direction; while _a difference in composition causes the substances in solution to move from the place of greater abundance toward places of less abundance_. 2. The liquids must be capable of wetting, or penetrating, the partition. If but one of the liquids penetrates the partition, the flow will be in but one direction. 3. The liquids on the two sides of the partition must readily mix with each other. *Osmosis at the Cells.*--In the body osmosis takes place between the blood and the lymph and between the lymph and the cells, the movements being through the capillary walls and the membranes inclosing the cells (Fig. 27). Oxygen and food materials, which are found in great abundance in the blood, are less abundant in the lymph and still less abundant in the cells. According to the principle of osmosis, the main flow of oxygen and food is from the capillaries toward the cells. On the other hand, the wastes are most abundant in the cells where they are formed, less abundant in the lymph, and least abundant in the blood. Hence the wastes flow from the cells toward the capillaries. *Solutions.*--Neither the blood plasma nor the lymp
PREV.   NEXT  
|<   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77  
78   79   80   81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   >>   >|  



Top keywords:

partition

 

liquids

 

osmosis

 
abundant
 
Osmosis
 

abundance

 
direction
 

composition

 

density

 

difference


motion
 

greater

 

materials

 

liquid

 

upright

 
capillaries
 

wastes

 

principle

 

membranous

 
solution

places

 
penetrating
 

wetting

 

capable

 

formed

 

denser

 

Solutions

 
Neither
 

opposite

 

penetrates


plasma

 

substances

 

According

 

capillary

 

Oxygen

 

inclosing

 

membranes

 

movements

 

readily

 

oxygen


filled

 

vessel

 

exchange

 

molecules

 

minute

 

exists

 
proportion
 

membrane

 

separates

 

dialysis