40 INTR OD UCTION 



environs, and between the different parts of the same cell, the 

 more powerful the osmotic effects, and as a result the greater 

 the capacity for accomplishing work. The storing up of insolu- 

 ble and indiffusible forms of substance, such as glycogen, fat, 

 and proteids, is an important factor in maintaining inequali- 

 ties in osmotic pressure, and in this way of increasing work 

 capacity. 1 



The relation of osmotic pressure and osmosis to physiological 

 problems is only beginning to be studied. It is apparent that 

 they must be of essential importance in absorption from the 

 alimentary canal, in absorption and excretion between the cells 

 and the blood stream, and in secretion by glandular organs ; 

 but it is also certain that they are no less important in all the 

 less obvious chemical and physical processes of the cell. These 

 matters will not be discussed here at length. 2 In pathological 

 processes osmotic pressure may play an equally important role, 

 and the facts discussed in the preceding paragraphs will be 

 alluded to frequently in subsequent chapters. 



COLLOIDS 3 



Since Graham in 1861 studied the differences between the 

 substances that did or did not diffuse readily through animal or 

 parchment membranes, soluble substances have been classified 

 in the two main groups of colloids and crystalloids, which dis- 

 tinction Graham believed separated two entirely different classes 



1 J. Traube has developed a theory of osmosis, depending upon surface ten- 

 sion which appears to be of much importance (Zeit. f. exper. Path. u. Ther. ; 

 1905 (2), 117). According to this theory the direction and speed of osmosis 

 are determined by the difference in surface tension between the fluids on the 

 two sides of a membrane, the fluid with the less surface tension passing towards 

 the one with the higher tension. Surface tension differs from osmotic pressure 

 especially in that the nature of the dissolved substance is of more importance 

 than the quantity, e. g., 1 gmw. of arnyl alcohol lowers surface tension as much 

 as 81 gmw. of methyl alcohol, although equivalent amounts of both produce 

 the same effect on osmotic pressure. On this theory is built up a conception of 

 physiological secretion and absorption, which considers that only fluids of lower 

 tension than that of the blood enter it, e. g., absorption from the gastrointes- 

 tinal tract is favored because bile and peptone both lower surface tension, etc. 

 For details see the original article cited. 



2 For further consideration of the subject of osmotic pressure in these rela- 

 tions see : Livingston, " The Role of Diffusion and Osmotic Pressure in Plants," 

 University of Chicago Press, Chicago, 1903 ; Czapek, " Biochemie der Pflan- 

 zen," Jena, 1903. Also, Hober, Cohen, and Hamburger, all previously cited. 



3 For full discussions of the nature of colloids see : Hober, u Physikalische 

 Chemie der Zelle," Leipzig, 1902 ; Pauli, Ergebnisse der Physiologic, 1904 

 (III, Abt. 1), 155; Mann, "Physiological Histology," Oxford, 1902. The 

 complete literature is collected and summarized by Aron in the Biochem- 

 isches Centralblatt, 1905 (3), pages 461 and 501. The relation of colloids to 

 the problems of immunity is reviewed by Zangger, Cent. f. Bakt. (ref.),19Q5 

 (36), 161. 



