CHAPTER XIV. 



METABOLISM AND THE DISTRIBUTION OF MATERIAL. 

 The Distribution of Water in the Normal Organism. 



THE earliest stages in the development of life are accompanied by 

 powerful processes of swelling which soon reach a maximum, and 

 then pass over into a shrinking, which becomes progressively greater, 

 until death occurs. In the cases of plants, the struggle for water be- 

 tween seed and soil starts with germination (A. MUNTZ*). Growing 

 and full-grown plants show a certain turgor, i.e., a fulness or tension 

 like a distended rubber balloon, while a dying plant is withered and 

 poor in water. 



A three months' human fetus contains 94 per cent water; at birth 

 the water content is from 69 to 66 per cent; in adult life 58 per cent. 1 

 I am not acquainted with any figures of the water content of the aged, 

 but it is generally and with justice assumed, that in old age, the 

 water content decreases; turgescence in general, and of the skin in 

 particular, is obviously lost. The organism, taken as a whole, dur- 

 ing its life evidently passes through the curves of swelling and shrink- 

 ing of an inelastic gel. In individuals of the same species, the water 

 content is probably fairly constant for the same period of life. 



The water content of the individual portions of plants and of simi- 

 lar organs of different plants varies remarkably. Though jelly-like 

 protoplasm contains from 60 to 90 per cent of water, the dry wall of 

 ligneous cells takes up from 48 to 51 per cent, while the jelly-like 

 membranes of nostocacese and palmellacese absorb as much as 200 

 per cent of water, according to NAGELI; on the other hand, cork 

 membranes have hardly any swelling capacity at all. 



The resistance offered to loss of water is exceptionally variable. 

 It may be said, with certain exceptions, that plants are much more 

 resistant than animals. Especially the lower forms of Me, particu- 

 larly the spores of bacteria, yeasts, algae, mosses and seeds may bear 

 almost complete dehydration without dying. Loss of water is often 

 of great biological significance for plants. It makes spores and seeds 

 less sensitive to changes of temperature; and in the case of some 



1 The greater water content of the individual organs of the newborn as con- 

 trasted with those of adults is especially evident from the tables of E. Bischoff.* 



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