COLLOIDS. 39 



For this reason it has been repeatedly stated that these salts are responsible 

 for the small differences in the osmotic pressure. By carefully washing 

 crystalline proteins from serum and egg-white, REID was able to prepare 

 bodies which gave finally no osmotic pressure in the osmometer. 1 In 

 opposition to this, MOORE and ROAF as well as LILLIE call attention to 

 the fact that the osmotic pressure of protein solutions is influenced 

 by the treatment which the protein received before the determination. 

 STARLING, 2 MOORE and PARKER, 3 MOORE and RoAF 4 and LILLIE, 5 using 

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

 ment before use (serum proteins, ovalbumin) , as well as REID 6 (with 

 hemoglobin) , 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 found a pressure of 3-4 mm. Hg. for a 1 per cent hemoglobin 

 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 

 aggregation 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 

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

 to its precipitation point and is probably united in large aggregations which 

 causes a lowering in the osmotic pressure. 



Filterability. Large particles suspended in a liquid can be removed 

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

 thicker must the filter be. Extensive experiments on the filtering of 

 colloids have been carried out by BECHOLD. S He used paper filters 

 which were impregnated with collodion dissolved in glacial acetic acid. 

 According to the concentration of the collodion solution filters of dif- 

 ferent porosity were obtained. The colloid solutions were pressed 

 through the filter by a pressure up to five atmospheres. It was shown 

 that all colloid solutions contained particles of various sizes. Never- 

 theless for every solution a filter could be prepared whose pores were 

 small enough to retain all the particles. In this manner BECHOLD was 

 able to classify the colloids in a series according to the size of the smallest 

 particles. He found that in general the inorganic colloids (Prussian 

 blue, platinum, iron oxide, gold, silver) form larger particles than the 



1 Journ. of Physiol., 31, 438, 1904. 5 Amer. Journ. of Physiol., 20, 127, 1907. 



2 Ibid., 19, 322, 1896. 6 Journ. of Physiol., 33, 12, 1905. 



3 Amer. Journ. of Physiol., 7, 261, 1902. 7 Bioch. Journ., 3, 422, 1908. 



4 Bioch. Journ., 2, 34, 1906. 8 Zeitsehr. f. physik. Chem., 60, 257, 1907. 



