282 THE PROPERTIES OF PROTOPLASM 



physical and chemical properties which are possessed by water and 

 carbon dioxide. Even the additional stability of the environment of 

 life which is brought about by the maintenance of constant temperature 

 in the homoiothermal animals, is dependent upon the unique specific 

 heat of water. The fitness of our environment for life is therefore 

 essentially dependent upon these substances. As Henderson has 

 pointed out, it is not that living matter has become adapted in an 

 evolutionary sense to this medium, although specific organs concerned 

 in the maintenance of the stability of the environment in higher 

 organisms, such as the kidney, may have been subject to evolutionary 

 adaptation. For the environment or the conditions from which it 

 inevitably arose long antedated life itself, and the earliest forms of 

 life must have been fitted to this environment no less exactly than the 

 later. A direct chemical interrelationship between life phenomena 

 and the particular type of environment in which they occur is thus 

 indicated. 



It is somewhat idle to speculate whether or not life could subsist 

 in some quite different environment with some other element such as 

 silicon or boron as a base instead of carbon. Such "life," if it could 

 correctly be so called, lies of necessity outside our experience. But 

 the absolute dependence of life as we know it upon water in the liquid 

 form and carbon dioxide in the gaseous form, renders the temperature 

 limits between which life can subsist excessively narrow in comparison 

 with the vast range of temperatures found in the various portions of 

 our universe. Of the 6500 degrees which separate the temperature of 

 interstellar space from that of the surface of the sun, only 65 or one 

 per cent, of the total range is suitable for the occurrence of life-pheno- 

 mena. In view of this exceedingly narrow margin upon which life 

 precariously depends, the probability of its presence in any other of the 

 bodies in our solar system must be regarded as exceedingly small. 

 Concerning the possibility of life in other suns or planets which may 

 be associated with them, we are of course in complete ignorance, but 

 Arrhenius has put forward the interesting hypothesis that life may be 

 transmissable, in the latent form which is embodied in bacterial spores, 

 from one part of the universe to another in association with cosmic 

 dust. Bacterial Spores have been experimentally shown to be exceed- 

 ingly resistant to desiccation and low temperatures, retaining their 

 ability to give rise to functionally active protoplasm so soon as they 

 encounter a favorable environment. The computations of Arrhenius 

 show that the known properties of certain bacterial spores are not 

 inconsistent with the view that they might survive a journey through 

 space, impelled by light-pressure, from one solar system to another. 

 If this view be correct, then the existence of life in any part of the 

 universe might sow the whole with seeds ready to develop at any mo- 

 moment at which the environment of a particular cosmic body becomes 

 suitable for the maintenance of the processes of functionally active life. 



