316 IMBIBITION AND EXHALATION. 



body, are regulated by the same conditions as in artificial experi- 

 ments, but they take place with infinitely greater rapidity, owing to 

 the movement of the circulating blood, and the extent of contact 

 existing between the bloodvessels and adjacent tissues. We have 

 already seen that the absorption of the same fluid is accomplished 

 with different degrees of rapidity by different animal substances. 

 Accordingly, though the arterial blood is everywhere the same in 

 composition, yet its different ingredients are imbibed in varying 

 quantities by the different tissues. Thus, the cartilages absorb 

 from the circulating fluid a larger proportion of phosphate of lime 

 than the softer tissues, and the bones a larger proportion than the 

 cartilages; and the watery and saline ingredients generally are 

 found in different quantities in different parts of the body. The 

 same animal membrane, also, as it has been shown by experiment, 

 will imbibe different substances with different degrees of facility. 

 Thus, the blood, for example, contains more chloride of sodium 

 than chloride of potassium ; but the muscles, which it supplies with 

 nourishment, contain more chloride of potassium than chloride of 

 sodium. In this way, the proportion of each ingredient derived 

 from the blood is determined, in each separate tissue, by its special 

 absorbing or endosmotic power. 



Furthermore, we have seen that albumen, under ordinary condi- 

 tions, is not endosmotic ; that is, it will not pass by transudation 

 through an animal membrane. For the same reason, the albumen 

 of the blood, in the natural state of the circulation, is not exhaled 

 from the secreting surfaces, but is retained within the circulatory 

 system, while the watery and saline ingredients transude in varying 

 quantities. But the degree of pressure to which a fluid is subjected 

 has great influence in determining its endosmotic action. A sub- 

 stance which passes but slowly under a low pressure, may pass 

 much more rapidly if the force be increased. Accordingly, we find 

 that if the pressure upon the blood in the vessels be increased, by 

 obstruction to the venous current and backward congestion of the 

 capillaries, then not only the saline and watery parts of the blood 

 pass out in larger quantities, but the albumen itself transudes, and 

 infiltrates the neighboring parts. It is in this way that albumen 

 makes its appearance in the urine, in consequence of obstruction to 

 the renal circulation, and that local oedema or general anasarca 

 may follow upon venous congestion in particular regions, or upon 

 general disturbance of the circulation. 



The processes of imbibition and exudation, which thus take 



