WATER ITS RELATION TO METABOLISM 259 



transmit the longer waves of light, and reflect and scatter in all 

 directions the shorter blue and violet ones. The scattered blue rays 

 give the blue colour to the heavens. At high altitudes the blue is 

 found to change towards black, and outside the atmosphere the sun 

 would appear not yellow but blue. The colourlessness of the land- 

 scape in intense sunlight as seen by direct vision is very noticeable 

 in contrast to the depth of colour seen in a reflection of the same 

 in water or in a mirror. This is due partly to the white light re- 

 flected from all surfaces without penetration colour being due to 

 reflection after penetration and absorption of certain rays partly 

 to irradiation. Any bright spot appears larger than it really is, 

 owing to the stimulus overflowing into the region of the retina which 

 borders that directly stimulated. The colours of sunrise and sunset 

 are due to the obliquity of the sun's rays, and their passage through 

 a far greater depth of atmosphere, whereby the more refrangible 

 rays are scattered by dust and vapour particles. 



Protoplasm contains almost 80 per cent, of water, and its vital 

 activity is inseparably bound up with this high percentage. The 

 water is in a state of chemical combination so that it can only 

 be separated by very high pressure or by processes of chemical 

 disruption, which, as a rule, are associated with coagulation and 

 death. Nevertheless the spores of bacteria, seeds, rotifers, &c., 

 can be dried, and after being kept inert for years, can be restored 

 to activity by the addition of water. It is a question whether life 

 continues to persist in some particle of moist protoplasm enclosed 

 by an impermeable dry envelope a cuticle formed by the drying 

 process or whether water is entirely removed from the chemical 

 combination without destruction of the protoplasmic molecule. 



The organs of different animals, taken free from fat, yield an 

 almost constant percentage of water. Thus, in the muscles of the 

 sheep, ox, swine, the percentage is 78-79, in those of the lobster 

 79, of the snail 78-79. There is also no great difference between 

 the various organs ; e.g. the blood contains 80 per cent., the liver 

 77-78 per cent., the spleen 78-79 per cent., the heart 78-79 

 per cent. Exceptions to this percentage are found only in tissues 

 modified by the storage of food material or for skeletal purposes 

 tissues, in other words, which have no direct share in the activities 

 of life. Thus the umbrella of the jelly-fish is so lightened by a 

 content of 95 per cent, water that it almost floats without 

 muscular effort. The percentage of water in the body of man is 

 about 63. 



