QUANTITY OF THE SWEAT. 389 



Every physician must have had opportunities of observing that 

 certain piyments sometimes occur in the sweat of patients ; thus 

 the body-linen of jaundiced persons who perspire freely, sometimes 

 assumes a yellow colour. Blue and red pigments have also been 

 observed in the sweat. 



It has been shown by the experiments of Milly, Jurine, 

 Ingenhouss, Spallanzani, Abernethy, Barruel, and Collard de 

 Martigny,* that gases, and especially carbonic acid and nitrogen, 

 are likewise exhaled with the liquid secretion of the sudoriparous 

 glands. According to the last named experimentalist, the ratio 

 between these two gases is very variable ; thus, in the gas 

 developed after vegetable food there is a preponderance of carbonic 

 acid, and after animal food an excess of nitrogen ; Abernethy 

 found that on an average the collective gas contained rather more 

 than two-thirds of carbonic acid, and rather less than one-third of 

 nitrogen. When the process of perspiration is especially active, 

 as, for instance, after strong bodily exercise, less gas is on the whole 

 exhaled. 



With regard to the method of analysing the sweat, we have 

 scarcely anything to add to the remarks already made (in various 

 parts of the first volume) respecting the determination of the 

 individual constituents contained in this secretion ; we must, how- 

 ever, especially recollect that its volatile constituents can only be 

 accurately determined by a careful examination : and again it 

 must riot be forgotten that the sweat very easily decomposes, and 

 gives rise to the secondary formation of ammonia. 



Numerous, and undoubtedly very careful, investigations have 

 been made regarding the absolute quantities of the substances 

 which are thrown off in a definite time by the sudoriparous glands 

 and the skin generally. We shall postpone any notice of those 

 investigations which, from the time of Sanctorius to that of 

 Scharling, have simultaneously included the cutaneous and the 

 pulmonary transpiration, and have estimated their sum collectively, 

 till we treat of the respiratory process. Cruikshank, Abernethy, 

 Dalton, and Anselmino, attempted in various ways to determine 

 the amount of the cutaneous secretion ; the most important, 

 however, was that which Anselmino adopted, of determining the 

 amount of the perspiration given off by a single extremity or by 

 a known extent of cutaneous surface, and then calculating how 

 much would be given off by the whole surface of the body ; but 

 independently of the circumstance that the other data for our 

 * Journ. de Physiol. T. 11, p. 1. 



