The observations made by Linings, in the climate of South Carolina, bear importantly on this subject. He found that while perspir ation, as might be expected, was most abund ant in the warm weather of summer, the urine diminished proportionally, and that the converse pertained for the winter. He ob served the perspiration to exceed the urine during seven months, and the urine the pers piration during five months of the twelve. The largest proportion of urine observed was 143 oz., which occurred in December. The largest proportion of perspiration was 130 oz., and was observed in September. The ingesta were to the perspiration as 2'18 to 1. The perspiration of the whole year was to the urine as 1 to 1'08. These experiments differ from those of Sanctorius and Rye, in showing that the urine exceeds the perspiration even in a hot climate.
On reviewing all that has been done by various experimenters, it appears doubtful whether, even in warm climates, the cutaneous exhalation exceeds that of the urine, and we ought most probably to regard it as consider ably below the quantity stated by Sancto rius. It must be remembered that, as in the experiments described above, the per spiration is estimated from the loss sustained by the body during a given period, atter the weight of faeces and urine discharge"; we have the pulmonary exhalation therefore included in the account, as well as the cutaneous.
Mr. Cruikshank made experiments which are free from this source of error. He placed his hand in a glass jar, making it air-tight by means of bladder fixed round his wrist and also bound tight to the mouth of the jar. He assumed that his hand presented a surface that of the whole surface of the body, and from that datum arrived at the conclusion that the exhalation from the skin was 7 lbs.
6 oz. in the 24 hours, which, under exercise, would amount to 12 lbs.
Mr. Abernethy made an experiment very similar to the above, but according to his cal culation, the exhalation for 24 hours would amount only to 2i lbs. This extraordinary difference may perhaps be accounted for by the fact that Mr. Abernethy continued his experiment six hours, and Mr. Cruikshank only one hour, and such being the case, the exhalation may have nearly ceased some length of time before six hours had elapsed, owing to the extremely moist atmosphere in which Mr. A.'s hand was placed. Cruikshank, it will be seen, would have to multiply by 24, and Abernethy by 4 only for the result of 24 hours. Thus the former would magnify the excess (obtained by the first hour affording a dryer atmosphere) into an important quan tity.
Lavoisier and Seguin have made excellent experiments with a view of ascertaining the amount of cutaneous exhalation. They en
closed the whole body in a varnished silk bag. There was a small opening to this, which was carefully cemented around the mouth of the subject of experiment. Thus all the mois ture from the lungs escaped, while the cuta neous exhalation was confined in the bag. By weighing the body before and after leaving the bag, the total loss from skin and lungs was ascertained. The amount of loss by the lungs was ascertained by weighing the person before he got into the bag and immediately before he left it. After a long series of ex periments conducted in this manner, Lavoi sier and Seguin found that the mean loss by pulmonary and cutaneous exhalation amounted to 18 grs. per minute, or 2 lbs. 13 oz. in 24 hours. Of this the pulmonary discharge was 15 oz., and the cutaneous exhalation 1 lb. 14 oz. This they regard, then, as the mean amount of daily perspiration. The greatest quantity of matter perspired in a minute, was 26.25 grs. troy, and the minimum 9 grs. Ex halation is increased by fluids, but not by solid food. It is at its minimum during meals, and at its maximum during digestion.
Under certain conditions vapour has been observed to escape from the body in very great quantity. Thus, Haller observed, when in the subterraneous caverns of Clausthal and Rammelsberg, that a distinct cloud or smoke could be perceived rising from the naked human figure.
Some diversity of opinion has prevailed among experimenters as to the gases which pass off from the body in company with the water, by the function of insensible perspira tion. Abernethy and Mackensie detected carbonic acid, and Collard de Martiguy found nitrogen in addition. These gases appear in variable quantity, and are sometimes alto gether absent. After muscular exertion, and after meals, they appear in great abundance. According to Trousset, Barruel, and Ingen houss, nitrogen is sometimes exhaled without carbonic acid. Monsieur Collard found that the cutaneous transpiration contained most nitrogen when an animal diet had been used, while carbonic acid prevailed vege table food was taken. This experimenter also satisfied himself that carbonic acid was evolved from the skin in a gaseous form, and need not be the result of oxydation of carbon by con tact with air, as he was able to collect it over water from the skin. The insensible cuta neous transpiration may be regarded then as composed of aqueous vapour, carbonic acid, and nitrogen gases ; the two latter not only varying in proportion like the first, but probably being sometimes absent, even in health, according to conditions of the organ ism, which are not yet sufficiently investi gated in relation to this subject.