SALT AND WATER IN LIFE AND GROWTH 123 



who first recognized the magnitude of this pressure in plant 

 cells. He also saw that such a pressure can be measured in 

 an osmometer of the type described in Figure 35. 



Through Pfeffer's work, Traube's basic ideas were re- 

 ceived and recognized in the official sciences. From that 

 time on work along this line has gradually spread. At 

 present, it is discussed from many diversified points of view. 



7. THE FLUID RETENTION IN THE HUMAN BODY IN 

 STARVATION AND WHAT CAUSES IT 



Let us return to our original problem, the perplexing 

 question of why the human body swells in some cases of 

 starvation and shrivels in others. We can indeed be proud 

 if this question can now be answered through the knowledge 

 acquired on our journey of exploration into the borderland 

 between living and non-living matter, where we followed 

 the trail blazed by the discoveries of Moritz Traube. 



Blood flows from the heart through the arteries, then 

 through the numerous narrow-gauge capillary tubes, and 

 finally back through the veins into the heart. The blood 

 vessels and the heart form a closed system surrounded by a 

 membrane everywhere. Blood can escape from this closed 

 system only where the coat of the vessel is very thin, as in 

 the capillaries. Fluid can break out here; not merely water, 

 but also the salts dissolved in the blood. However organic 

 matter, particularly the dissolved protein, cannot easily 

 escape through the thin capillary walls. (Fig. 36.) 



Since the heart through its contractions exerts a pressure 

 upon the blood, one might guess that fluid would be pushed 

 through the thin capillary wall, run into loose spaces of the 

 body, such as exist under the skin, and cause tissues to 

 swell, as is the case in certain diseases. What force keeps 

 the fluid in the capillaries? 



We again consider the principles of osmosis. Any dis- 

 solved substances in the blood which cannot pass through 



