OF MOISTUEE AS A CONDITION OF VITAL ACTIVITY. 101 



this tree is naturally found only in the southern parts of India ; and the 

 success of its cultivation in this northerly situation is entirely due to 

 its being sheltered by the numerous buildings within the lofty palace 

 wall, surrounded by almost a forest of trees, and receiving the benefit 

 of perpetual irrigation from a branch of the canal wjiich flows through 

 the garden. 



155. In regard to the influence of external moisture upon Animal 

 life, there is much less to be said ; since the mode in which fluid is re- 

 ceived into the system is so entirely different. It may be remarked, 

 however, that Animals habitually living beneath the water, like sub- 

 merged Plants, are usually incapable of sustaining life for any length 

 of time when removed from it, in consequence of the rapid loss of fluid 

 which they undergo from their surface. It is, however, by the desic- 

 cation of the respiratory surface, preventing the due aeration of the 

 blood, that the final result is for the most part, occasioned ; since we 

 find that when there is a special provision to prevent this, as in the 

 case of certain Fishes and Crustacea, the animals can quit the water 

 for a great length of time. There can be no doubt that the amount of 

 Atmospheric moisture is one of those conditions, which are collectively 

 termed climate, and which influence the geographical distribution of 

 Animals, no less than that of Plants. But it is difficult to say how far 

 the variations in moisture act alone. There can be no doubt, however, 

 of their operation ; for every one is conscious of the effect, upon his 

 health and spirits, of such variations as take place in the climate he 

 may inhabit. The two principal modes in which these will operate, will 

 be by accelerating or checking the exhalation of fluid from the skin and 

 from the pulmonary surface; for when the air is already loaded with 

 dampness, the exhaled moisture cannot be carried off with the same 

 readiness as when it is in a condition of greater dryness ; and it will 

 consequently either remain within the system, or it will accumulate and 

 form sensible perspiration. 



156. Now each of these states may be salutary, being the one best 

 adapted to particular constitutions, or to different states of the same 

 individual. A cold drying wind shall be felt as invigorating to the 

 relaxed frame as it is chilling to one that has no warmth or moisture to 

 spare; on the other hand, a warm damp atmosphere, which is refresh- 

 ing to the latter, shall be most depressing to the former. All who have 

 tried the effect of closely-fitting garments, impervious to moisture, are 

 well aware how oppressive they soon become ; this feeling being de- 

 pendent upon the obstruction they occasion to the act of perspiration, 

 by causing the included air to be speedily saturated with moisture. 

 When the fluids of the system have been diminished in amount, either 

 by the suspension of a due supply of water, or by an increase in the 

 excretions, there is a peculiar refreshment in a soft damp atmosphere, 

 or in a warm bath, which allows the loss to be replaced by absorption 

 through the general cutaneous surface. The reality of such absorption 

 has been placed beyond all doubt, by observations upon men, who had 

 been exposed to a hot dry air for some time, and afterwards placed in 

 a warm bath ; for it was found that the system would by this unusual 



