CELLS AND TISSUES. 37 



between the two (HEDIN, GRYNS). A part of these 

 exceptions could be explained by HEDIN, and more 

 especially by KOPPE, on the ground that the crystalloids 

 permeate the red blood-corpuscles more or less perfectly. 

 KOPPE has taken the following stand: The solution of a 

 red blood-corpuscle is analogous to the bursting of a 

 balloon filled with gas in a rarefied atmosphere. This 

 bursting will occur also when the space about the balloon 

 is filled with a gas that can pass through the wall of the 

 balloon, for it cannot under these circumstances counter- 

 act the pressure existing within the balloon: In this 

 way is explained the laking of blood in even the most 

 concentrated solutions of substances which are able to 

 pass into the red blood-corpuscles, such as urea. 



If this simple conception, deduced from the analogy 

 between gas pressure, and osmotic pressure, is strictly 

 tenable, then the addition of substances which lake 

 red blood-corpuscles (such as urea) to salt solutions 

 having a concentration in which the haemoglobin just 

 manages not to pass out of the corpuscles should be 

 without effect, since the relative osmotic conditions 

 within and without the cells remain unchanged. This is, 

 however, not the case ; such solutions also become colored 

 red. Whenever urea has been added to a NaCl solu- 

 tion a much higher concentration of the latter is required 

 to keep the red blood -corpuscles of the horse from losing 

 their haemoglobin than when pure NaCl is used. The 

 differences in concentration varied in a series of experi- 

 ments between 0.005 an d o.oi molecular NaCl, and were, 

 strange to say, not markedly influenced by an increase 

 in the concentration of the Urea from 0.25 to i .00 molecular. 



Not until thorough investigations have been made 



