COLLOIDS. 13 



rounding sea water (A = 2.3) and varies with the quantity of salt in the 

 water (BoiTAZZi). Jn lower fishes (Selachii) the osmotic pressure 

 of the blood is equal to the surrounding medium, and in higher fishes 

 (Teleostomi) lower (A = 1.0) (BOTTAZZI). In Selachii the osmotic 

 pressure of the blood is chiefly due to urea (ScHROEDER). 1 



In sea fishes as well as fresh-water fishes, for example, the eel, a lower 

 osmotic pressure (A = 0.41) is found when kept in fresh water than 

 when kept in sea water (A = 0.55) 2 . In lower sea animals the osmotic 

 pressure is equal to the surrounding medium, while higher animals are 

 independent of the surroundings. HOBER calls attention to this condi- 

 tion and points out the analogy with the body heat of the various 

 animals. 3 



If we pass to other body fluids we must mention that the lymph 

 shows a somewhat higher osmotic pressure than the blood, and this is 

 due to the lymph taking up from the tissues metabolic products hav- 

 ing a low molecular weight. 4 Milk and bile have the same osmotic 

 pressure as the blood, 5 while saliva has a lower pressure. 6 The urine 

 of man and mammalia generally has a much higher osmotic pressure 

 than the corresponding blood. 7 For human urine A varies between 1.3 

 and 2.3. After abundant drinking as well as under pathological con- 

 ditions (diabetes insipidus) the osmotic pressure of the urine can be lower 

 than the blood. In regard to the osmotic pressure of animal fluids under 

 normal and pathological conditions we refer to the work of KORANYI 

 and RicHTER. 8 



n. COLLOIDS. 



The word colloid originated with GRAHAM, who included in this name 

 different substances which did not have the property of diffusing through 

 .an animal membrane. In opposition to this GRAHAM called those 

 bodies which passed through a membrane, crystalloids, because they 

 were as a rule crystalline, a property which with few exceptions does 

 not belong to the colloids. 9 GRAHAM included soluble silicic acid among 



1 Bottazzi, Archives ital. de biol. 28, 61 (1897). Schroeder, Zeitschr. f. physiol. 

 Chem. 14, 576 (1890). 



2 Dekhuisen, Arch, ne'erland, 10, 121 (1905); Quinton, Compt. rend. soc. biol., 

 57, 470, 513 (1904). 



3 Physik. Chem. d. Zelle u. Gewebe, 3. Aufl. 353, (1911). 



4 Leathes, Journ. of Physiol., 19, 1 (1895). 



6 Dresser, Arch. f. exp. Path. u. Pharm., 29, 303 (1892). 



6 Nolf, Traveaux du lab. de phys. de Liege, 6, 225 (1901). 



7 Kora"nyi, Zeitschr. f. klin. Med., 33, 1 (1897), 34, 1 (1898). 



8 Physikalische Chemie und Medizin. Leipzig (1907). 



9 Ann. d. Chem. u. Pharm., 121, 1 (1862) as well as Ann. de chim. et de Phys. (4), 

 3, 127 (1864). 



