278 The Earlier Theories of Edema [Dec. 



stituents of the blood. Senator's (1868) experimental results led 

 him to advocate the theory of Cohnheim. Hamburger (1895) 

 also Supports Cohnheim's theory. 



It is obvious from this brief review, that for about 100 years 

 there have been two main ideas on the cause of edema: First, 

 changes in the character of the blood; second, changes in the perme- 

 ability of the vessel walls. While no doubt both of these influences 

 are important factors in edema, the parts played by the tissues them- 

 selves must not be overlooked. 



Loeb (1898) claimed that the tendency to transudation of fluid 

 into the tissues in edema is greater than that into the blood and 

 lymph, and that therefore the cause of edema must be either an 

 increase in the osmotic pressure of the affected tissue or a decrease 

 of the osmotic pressure in the circulatory system. Loeb demon- 

 strated the possibility of a rapid change in the osmotic pressure 

 of tissues, thus showing that the forces which (according to the 

 filtration theory) are able to produce edema are wholly inadequate. 

 The osmotic pressure of 0.7 per cent. sodium chlorid Solution 

 amounts to 4.9 atmospheres, which is twenty times more than the 

 blood pressure. Only a trace of acid or alkali in muscle increases 

 the osmotic pressure to such an extent that the muscle becomes 

 edematous in 0.7 per cent. salt Solution. By tetanizing muscle, its 

 osmotic pressure increases one atmosphere and through the ori- 

 ginal loss of water, chemical changes take place in the muscle which 

 raise its osmotic pressure twenty-five atmospheres. Welch never 

 obtained a rise of more than i/io of an atmosphere, so it is easily 

 seen how much more powerful the change in the osmotic pressure 

 is, as compared with circulatory changes. Loeb thinks that blood 

 and epithelial cells are present in edematous fluids as a result of 

 morphologic changes in the blood vessels. He believes these 

 changes are brought about by the same poisons which produce the 

 increase in osmotic pressure and has shown that these substances 

 may be produced by a lack of oxygen. 



In Order to test the filtration theory Loeb made the following 

 experiment : The circulation in a bind leg of a f rog was stopped 

 by means of a ligature. The ligatured extremity, when immersed 

 in water, increased in weight : after 16 hours, 2-3 per cent.; after 



