18 BIOLOGY: GENERAL AND MEDICAL 



"elements" Astronomy, however, shows us that the 

 primitive form of matter is gaseous and leads us to infer 

 that it is only through prolonged integration and differen- 

 tiation that the "elements" of the chemist have been 

 produced. 



Of the cosmical theories the . nebular hypothesis of 

 Kant and Laplace seems to be the one best suited to 

 the present thought, in spite of the more recent theories 

 that the heavenly bodies including our planet have been 

 formed by the coming together of ice-cold meteors, or by 

 gradual accretion through the continued accession of cold 

 planetary matter in space. 



According to the "nebular hypothesis" space is filled 

 with matter in every conceivable state of integration and 

 disintegration, its most primitive form being that of 

 gaseous vapor in a state of incandescence. According to 

 fixed laws, the forces of the universe act upon this gas- 

 eous vapor until it gradually collects more and more 

 locally to form nebulous masses such as can be seen in 

 various of the constellations. Through infinite time the 

 nebulae become more and more condensed until, in obe- 

 dience to the continually operating forces, they begin 

 to rotate more and more uniformly, their vaporous 

 particles to approximate more and more closely, and 

 finally to coalesce to form fiery masses whose progressive 

 integration passes from the gaseous to the fluid and 

 finally to the solid state, and the formation of definite 

 heavenly bodies. 



When the forces acting upon the nebulous matter are 

 uniform a single body may be produced, but when they 

 are conflicting several may be formed, the smaller 

 rotating about the larger in definite systems. The 

 smaller bodies of the system are subject to the most 

 rapid subsequent changes, so that in any planetary 

 system bodies in all stages may be observed. This is, 

 for example, supposed to be the state of our own solar 

 system, in which the sun is still a gaseo-liquid incandes- 

 cent body, some of the larger planets semi-solid, the 



