60 MECHANISM OF ABSORPTION. 



by two opposite degrees of activity of the circulation. 

 For when the mass of blood is much augmented, the 

 obstacles which naturally oppose its free passage 

 through the smaller vessels are materially increased, 

 at the same time that the action of the heart is 

 slower and more laboured than in health. Conse- 

 quently, the proportion then existing between the 

 moving power and the mass to be moved is un- 

 favourable to a rapid circulation ; and we may thus 

 explain the slower action of poisons after he had 

 injected a quantity of water into the veins. Whereas, 

 after bleeding, or any other large evacuation, the 

 whole of the arteries contract as the quantity of 

 blood in the system diminishes, so as to form a 

 series of narrower tubes, and the heart being relieved 

 of a part of its load, after the first shock is over, 

 increases the rapidity of its contractions so much 

 that a more rapid circulation of the blood must 

 necessarily result. 



There are two parts of the animal economy where 

 the process of absorption is actively carried on, and 

 where some beautiful modifications of this principle 

 are exemplified. I have said that compression of the 

 blood within its vessels causes effusion; it should 

 follow, therefore, that the compression of an external 

 fluid against membranous tubes, while traversed by 

 a rapid stream, will promote absorption ; and such 

 is known to be the case. The influence of pressure 

 in causing the absorption of morbid effusions in the 

 human body is well known, and its application is 

 seen in daily practice. In the intestines, through 

 which the bodies of animals obtain all their nourish- 



