516 DISEASES OF THE SKIN. 



augmented. There had been no profuse sweating; and it is veiy 

 probable that, besides the conditions mentioned above, there are others 

 which likewise serve to increase the imperceptible perspiration. 



A diminution of the insensible perspiration is probably of common 

 occurrence, for instance, in a very cold or very moist atmosphere ; but 

 hitherto, this fact has only been demonstrated directly by weighing, in 

 cases of diabetes mellitus. 



We know nothing positive about the qualitative changes in the 

 cutaneous evaporation, and can merely suppose that in febrile dis- 

 orders this excretion not only increases in quantity, but is altered in 

 its composition. That such a change does take place seems to be indi- 

 cated by the peculiar odor emitted by the gaseous perspiration of pa- 

 tients suffering from the acute exanthemata. 



The secretion of sweat is much increased in most people when they 

 ire exposed to certain influences. Both healthy persons, and persons 

 suffering from chronic diseases free from fever, if weighed before and 

 ifter a course of profuse artificially-induced sweating, are found some- 

 times to have lost four or five pounds' weight in a few hours. We 

 have no precise knowledge of the conditions which regulate the pro- 

 duction of sweat. Healthy persons sweat profusely when covered by 

 blankets and made to drink copiously ; but in most febrile diseases 

 they do not perspire at all, though treated in the same manner ; while 

 there are other disorders attended by fever (not merely the inexpli- 

 cable sudor angelicus of the middle ages, but many cases of pneumonia 

 and rheumatism), in which the sweating is profuse throughout the 

 whole attack. That the secretion of sweat, like that of the saliva, is 

 dependent upon nervous influence, is evident from the effect which the 

 mental emotions exert upon its production. Some persons perspire 

 more readily and profusely than others. An excessive tendency to 

 perspiration is called hyperidrosis. It generally depends upon un- 

 known causes ; but in some instances it unmistakably is a consequence 

 of repeated artificially-induced diaphoresis. Barensprung mentions 

 many examples of hyperidrosis proceeding from the above cause. I 

 myself have never noticed any great increase in the secretions of the 

 skin at the commencement of a course of diaphoretics, and have only 

 observed it in persons who had been under treatment for some time, 

 and hence can confirm the assertion that profuse sweating augments 

 the tendency to diaphoresis. When the secretion of the sudoriferous 

 glands cannot escape, owing to obstruction of the gland-ducts, or be- 

 cause the latter are incapable of transmitting all the secretion formed, 

 it emerges around the sweat-duct under the epidermis, and, lifting the 

 latter, forms small, clear vesicles containing an acid liquid, which are 

 sailed sudamina. Obstruction of the efferent ducts of the sudoriferous 



