THE SMALLEST PARTICLES OF MATTER 37 



matter may be scattered in space between the nebulas does not 

 dim appreciably the most distant ones now visible. Dropping this 

 from consideration, the concentration of matter in the visible 

 region figures out to about one gram per 10 30 cubic centimeters, 

 which is equivalent to one grain of sand in each volume of space 

 equal to that of the earth. 28 



Plummeting down to our own tiny but (to us) important levels, 

 we find that life depends upon a great variety of ordered chemical 

 reactions which are rather limited in space, mass, and time. Living 

 units have masses ranging from the molecular or near-molecular 

 up to the immense bulk of the whale or elephant. The chief 

 chemical elements involved are carbon, hydrogen, oxygen, nitro- 

 gen, phosphorus, sulfur, sodium, potassium, calcium, iron, mag- 

 nesium, and manganese; but quite a number of other elements 

 are also essential or incidental, in amounts small in percentage but 

 large in numbers of atoms, e.g., copper, zinc, fluorine, vanadium 

 and molybdenum. From this quintessence of dust, living units 

 have emerged on our tiny planet which in the slow course of time 

 developed brains and bodies with which they can receive and 

 order sense impressions, remember, think, and reason. How all 

 this happens, no one knows; but the result is undoubted, irrespec- 

 tive of what words are used to describe it — mind, psyche, soul, etc. 

 It is recognized in our laws, is studied by psychologists, psychia- 

 trists, sociologists, and teachers, and dominates the daily life of 

 every one of us. 



In a biographical sketch of Emil Dubois-Reymond, apparently 

 written by Sir Michael Foster, 29 the following is quoted as the 

 dominant note of "Elements of Physiology" by Johannes Miiller, 

 central figure of modern physiology: 



"Though there appears to be something in the phenomena of 

 living beings which cannot be explained by ordinary mechanical, 

 physical or chemical laws, much may be so explained, and we may 

 without fear push these explanations as far as we can, so long as 

 we keep to the solid ground of observation and experiment." 



Since we now have a continuity of successive levels of material 

 structure down to the nuclear level, there is no longer any "no- 

 man's land" where material mysteries of life can escape scientific 

 investigation. Our present knowledge, based on observation and 

 experiment, indicates that the simplest living units are in the 

 molecular or near-molecular range. The information assembled 

 in this book indicates that many, if not all the basic material facts 



