66 PHYSIOLOGY CHAP. 



equally distributed among the different tissues ; a sort of struggle 

 for existence goes on between them, some being consumed and 

 liquefied for the benefit of others, which continue to exist as 

 parasites, and are even able to reproduce themselves (Luciani). 

 The process of inanition in the higher animals and man wjll, 

 however, be treated in detail later on. 



II. Another condition no less indispensable to metabolism 

 is water, which infiltrates the living protoplasm in large quantities, 

 rendering it soft or semi-fluid. In order to realise the importance 

 of water to the vital functions, we need only consider the 

 consequences of natural or artificial desiccation in unicellular 

 organisms. Within certain limits the intensity of metabolism 

 increases or decreases with the increase or decrease of the water 

 content of the living matter, while beyond those limits vital 

 activity ceases altogether. In the great majority of plants, 

 natural dryness of environment is sufficient to cause death. Many 

 mosses, lichens and algae, however, which live on naked rocks are 

 able to support the drought of summer without injury. Seeds 

 and spores, in particular, when removed from the plant, may be 

 kept in a dry state without losing their capacity, for germination. 

 It was formerly stated that the wheat found with the Egyptian 

 mummies retained its power of germinating after more than two 

 thousand years; but this fact was disproved by the famous Egypto- 

 logist Mariette. It has, however, been demonstrated that spores 

 of mosses and the seeds of Mimosae, kept in a dry state for over 

 sixty years in a herbarium, were perfectly capable of germination ; 

 other seeds, on the contrary, lose their vitality after one year, 

 others again after a few days, while others will not tolerate any 

 desiccation, e.g. the seeds of Salix. 



Some groups of animals can be kept for years in a desiccated 

 state without losing the faculty of awakening to life a few 

 moments after they are moistened again (Preyer's anabiosis). 

 Among these are the so-called Jftoti/erae, small crustaceans, and the 

 Tardegrada, arachnoids resembling mites, which live in the moss 

 and dust of roofs, as discovered by Leeuwenhoek (1719), who first 

 described this remarkable phenomenon. Also the Anguillulae 

 of mildewed wheat, on which Spallanzani (1776) made many 

 curious experiments of repeated anabiosis. Lastly, the greater 

 part of the bacteria, particularly in the spore state, come under 

 the same category. 



It is not easy in any of these cases of apparent death to 

 determine whether there is absolute suspension of metabolism, a 

 true latent or potential life, or a metabolism reduced to the 

 lowest terms, i.e. to the state which Spallanzani was the first to 

 characterise as minimal life. To decide the question, it is neces- 

 sary to determine whether these organisms in a state of apparent 

 death exhibit any trace of respiratory exchange, i.e. of absorption 



