32 INTRODUCTION. 



in our manipulations, the principle is not brought near a state 

 of chemical purity, but is essentially and radically changed. 



The quantity of water which each organic substance con- 

 tains is important / and it is provided that this quantity, 

 though indefinite, shall not exceed or fall lelow certain Urn- 

 its. The truth of this proposition is made evident from the 

 following facts : In the first place, all organs and tissues must 

 contain a tolerably definite quantity of water to give them 

 proper consistence. The evils of too great a proportion of 

 water in the system, and consequently a diminution of solid 

 elements, are well known to the practical physician. Gen- 

 eral muscular debility, loss of appetite, dropsies, and various 

 other indications of imperfect nutrition, are among the re- 

 sults of such a condition ; while a deficiency of water is im- 

 mediately made known by the sensation of thirst, which 

 leads to its introduction from without. 



The fact that water never exists in any of the fluids, semi- 

 solids, or solids, without being combined with inorganic salts, 

 and especially chloride of sodium, is one reason why its pro- 

 portion in various situations is to a certain extent constant. 

 The presence of these salts influences, in the semi-solids at 

 least, the quantity of water entering into their composition, 

 and consequently regulates their consistence. A very simple 

 experiment shows this with reference to the chloride of 

 sodium. If a piece of muscle be placed in a strong solution 

 of common salt, as in salting meat, it becomes harder, and 

 loses a portion of its water of composition ; while exposed 

 to the action of pure water, it absorbs a certain quantity and 

 becomes softer. The nutrient fluid of the muscles during 

 life contains water with just enough saline matter to pre- 

 serve their normal consistence. This action of saline matters 

 is even more apparent in the case of the blood corpuscles. 

 If pure water be added to the blood, these bodies swell up 

 and are finally dissolved ; while if we add a strong solu- 

 tion of salt, they lose water, and become shrunken and 

 corrugated ; but their natural form and consistence can 

 be restored, even after they have been completely dried, by 



