COLLOIDS. 17 



STARLING, 1 MOORE and PARKER, 2 MOORE and ROAF S and LiLLiE, 4 using 

 protein preparations which had not been exposed to any strong treat- 

 ment before use (serum proteins, ovalbumin), as well as REID 5 (with 

 haemoglobin), have been able to detect a low osmotic pressure and 

 indeed by the aid of osmometric methods. According to STARLING, 

 the proteins of the serum correspond to a pressure of 30-40 mm. Hg. 

 and REID G found a pressure of 3-4 mm. Hg. for a 1 per cent haemoglobin 

 solution. 



The influence of added bodies upon the osmotic pressure has been tested by 

 LILLIE by adding the substance to be tested in the same percentage concentration 

 to the inner and outer fluids. It was found that non-electrolytes were without 

 action while acid and alkalies increased the osmotic pressure of gelatin solutions, 

 while salts lowered the pressure of gelatin as well as ovalbumin solutions. ADAM- 

 SON and ROAF 7 arrived at similar results in regard to alkalies and acids. Besides 

 this, LILLIE found that the osmotic pressure was dependent upon the past history 

 of the colloid. Warming as well as shaking the solutions seems to change the 

 aggregate condition, which returns very slowly or not at all. The changes 

 in the osmotic pressure produced by salts, LILLIE explains by a change in the 

 aggregate condition of the colloid, by the addition of salts it is brought closer 

 to its precipitation point and is probably united in large aggregations. In this 

 way the number of particles is diminished and, as this number must be important 

 for the osmotic pressure, this pressure is lowered. In agreement with this 

 the above mentioned influence of acids and alkalies upon the osmotic pressure of 

 gelatin can be explained by an increase in the particles. 8 



As we have seen above the determination of the elevation of the boil 

 ing-point or the depression of the freezing-point is the simplest way 

 for estimating the osmotic pressure of a crystalloid substance in solution. 

 If such determinations are made with a colloidal solution then unmeas- 

 urable results are found for the elevation of the boiling-point or the depres- 

 sion of the freezing-point. This indicates, as above stated, that the 

 molecules or the particles must be very large. F. KRAFT 9 found no 

 elevation of the boiling-point for soaps in watery solution but obtained 

 values which correspond to the calculated molecular weights when the 

 soaps were dissolved in alcohol. Therefore the soaps are colloidal in 

 watery solution and crystalloidal bodies in alcoholic solution. 



Filterability. Large particles suspended in a liquid can be removed 

 from the fluid by filtering. The finer the suspended particles are the 



1 Journ. of Physiol., 19, 322 (1896). 



2 Amer. Journ. of Physiol., 7, 261 (1902). 



3 Bioch. Journ., 2, 34 (1906). 



4 Amer. Journ. of Physiol., 20, 127 (1907). 

 Journ. of Physiol., 33, 12 (1905). 



6 Bioch. Journ., 3, 422 (1908). 



7 Ibid. 



Pauli, Roll. Zeitschr., 7, 241 (1900). 



9 Ber. d. d. chem. Gesellsch., 29, 1328 (1896); 32, 1584 (1899). 



