102 EXTERNAL CONDITIONS OF VITAL ACTIVITY. 



means supply the deficiency, which had been created by the previous 

 increase in the transpiration. 



157. The effect of a moist or dry atmosphere, then, upon the Animal 

 body, cannot be by any means unimportant; although, as we shall 

 hereafter see, there exists in it a series of the most remarkable provi- 

 sions for regulating the amount of its fluids. The influence of atmo- 

 spheric moisture, however, is most obvious in disordered states of the 

 system. Thus in persons who are subject to the form of Dyspepsia 

 called atonic, which is usually connected with a generally-relaxed con- 

 dition of the system, a very perceptible influence is experienced from 

 changes, in the quantity of atmospheric moisture ; the digestive power, 

 as 'well as the general functions of the body, being invigorated by dry- 

 ness, and depressed by damp. Again there is no doubt that, where a 

 predisposition exists to the Tuberculous Cachexia, it is greatly favoured 

 by habitual exposure to a damp atmosphere, especially when accom- 

 panied by cold : indeed it would appear, from the influence of cold damp 

 situations upon animals brought from warmer climates, that these two 

 causes may induce the disease, in individuals previously healthy. On 

 the other hand, there are some forms of pulmonary complaints, in which 

 an irritable state of the mucous membrane of the bronchial tubes has a 

 large share ; when this irritation presents itself in the dry form, a warm 

 moist atmosphere is found most soothing to it ; whilst a drier and more 

 bracing air is much more beneficial, when the irritation is accompanied 

 by a too copious secretion. 



158. Although, as already stated, no .vital actions can go on without 

 a reaction between the solids and fluids of the body, yet there may be 

 an entire loss of the latter, in certain cases, without necessarily destroy- 

 ing life ; the structure being reduced to a state of dormant vitality, in 

 which it may remain unchanged for an unlimited period ; and yet being 

 capable of renewing all its actions, when moisture is again supplied. Of 

 this we find numerous examples among both the Vegetable and the Ani- 

 mal kingdoms. Thus the Mosses and Liverworts, which inhabit situa- 

 tions where they are liable to occasional drought, do not suffer from 

 being, to all appearance, completely dried up; but revive and vegetate 

 actively, as soon as they have been thoroughly moistened. Instances 

 are recorded, in which Mosses that have been for many years dried up 

 in an Herbarium, have been restored by moisture to active life. There 

 is a Lycopodium (Club-Moss) inhabiting Peru, which, when dried up for 

 want of moisture, folds its leaves and contracts into a ball ; and in this 

 state, apparently quite devoid of animation, it is blown hither and thither 

 along the surface by the wind. As soon, however, as it reaches a moist 

 situation, it sends down its roots into the soil, and unfolds to the atmo- 

 sphere its leaves, which, from a dingy brown, speedily change to the 

 bright green of active vegetation. The Anastatica (Rose of Jericho) is 

 the subject of similar transformations ; contracting into a ball, when 

 dried up by the burning sun and parching air ; being detached by the 

 wind from the spot where its slender roots had fixed it, and rolled over 

 the plains to indefinite distances ; and then, when exposed to moisture, 

 unfolding its leaves, and opening its rose-like flower, as if roused from 

 sleep. A blue Water-Lily abounds in several of the canals at Alexan- 



