10 TRANSITION FROM HEALTH TO DISEASE. 



eliminate them. (Dr. Watson's Lectures, ' Med. Gaz./ 

 1840.) 



The ExcKETORiEs are the intestines, the kidneys, the lungs, 

 and the skin. The extensive surface for secretion which 

 the intestines present^ and the quantity of fluids or iyites- 

 tinal juice they separate from the blood, j^^stly entitle them 

 to the first place amongst excretories. The kidneys are 

 likewise (in horses particularly) active in extracting super- 

 fluous matter from the blood ; and the lungs and skin both 

 tend to relieve the system by a discharge of aqueous ex- 

 halations. In this manner all useless or redundant matters 

 are got rid of; the blood being all the while the vehicle 

 through which these various ends are accomplished. 



The fluids that leave the blood may be considered under 

 a threefold division : 



1. Those which are expended in the growth and mainte- 

 nance of parts, some of them becoming fixed and solid ; 

 others retaining their fluid condition. 



2. Those that are employed in aid of some definite function 

 of the body, as the saliva, gastric juice, &c. Now, the in- , 

 crease or diminution of these secretions may either be the 

 result of disease, or may cause disorder. 



3. Those which are separated from the blood merely to 

 be excreted, as the urine, certain secretions from the bowels, 

 and from the bronchi and skin. (Dr. Watson's Lectures, 

 'Med. Gaz.,' 1840.) 



The blood itself is liable to undergo certain morbid 

 changes : 



1. It may vary in quantity, both in respect to the whole 

 system, and in respect to particular organs and tissues. 



2. Closely connected with these difi'erences in quantity is 

 the variety which is observable in regard to the proportions 

 between the several constituents of the blood — thinner, less 

 rich in fibrine or colouring matter. 



3. Independently of changes in the relative proportions 

 of its constituents, the blood is liable to great change in its 

 chemical composition, and, therefore, in its physical quality. 

 This appears to be the case in sea-scurvy and purpura. 



