in relation to Disease. 29 



power of accommodation in the body, depending on the gene- 

 ration of animal heat, and on the functions of the lungs and of 

 the skin, provides in the healthy state against all which are not 

 in excess. But where these functions are impaired, or the body 

 otherwise disordered, every such change has influence ; either 

 by disturbing the balance of circulation between the external 

 surface, and the membranes or different glandular structures 

 within the body ; — or by checking or augmenting the discharge 

 of perspirable matter ; — or in part, it may be, by more imme- 

 diate action on the nervous system ; though of this we have less 

 certain proof. 



The degree in which external cold may alter the balance of 

 circulation, — directly, by contracting the capillaries and smaller 

 arteries of the surface ; or indirectly, by the effect of this altered 

 balance upon the action of the heart itself, — is scarcely enough 

 regarded in its various details.* It is to be presumed, on the 

 most common grounds of estimation, that the differences thus 

 made may vary, (according to the degree of cold and the powers 

 of re-action from within) from the smallest assignable amount 

 to that of several pounds of blood, changed in its manner of 

 distribution through the vessels of the body. The importance 

 of such fluctuations must be obvious on the most general view. 

 And they include, it may be added, not merely the repulsion 

 of blood from the surface by the contraction of the capillaries, 

 but also the effects of the re-action and return of blood to the 

 part ; the latter consequences often very remarkable in their 

 influence on the bodily functions. 



The tendency of sudden changes of temperature to produce 

 topical inflammation, is doubtless owing chiefly to these disturb- 

 ances in the balance of circulation, which arise from changes, 

 general or partial, in the capillaries of the surface. Rheumatic 

 affections, whether inflammatory or not, are usually attributed 

 to the same cause ; rightly, as respects some states which bear 

 the name ; not so, as to others, which are undoubtedly of dif- 

 ferent origin. Many disorders of the serous and mucous 



* The experiments of M. Poiseuille, in his treatise on capillary circular 

 tion, confirmed by those of M. Magendie, show the efiect of a low tempera- 

 ture in retarding or preventing the passage of blood through these extreme 

 vessels. 



