1897.] Natural Impulses. 587 
known fact, that mineral matter is subject to similar con- 
straints, being forced, when crystallizing, to assume certain in- 
variable forms. Every crystalline body has its peculiar shape 
varying only by the addition of planes belonging to forms of 
the same system. Compounds of different ingredients, but of 
similar constitution, are frequently found to appear in the 
same forms, as is seen in the class of compounds comprised by 
the name of “alum.” Whenever a body is found crystallizing 
in several systems, a chemical difference, although perhaps a 
slight one, may generally be assumed. But in identical bodies 
polymerisation, or multiplication of atoms in a molecule, is a 
frequent cause of variationsin form. It is one of the merits of 
the new doctrine of stereo-chemistry to have given the hint, 
that molecules of compounds as well as of elementary bodies, 
contain their atoms arranged in certain directions given by the 
prevailing chemical attractions. In accordance with this view 
every molecule may be represented by a certain stereometric 
form, be it a tetrahedron, an octahedron, a cube, etc. The 
attractions diverting accumulation of atoms in a molecule also 
govern the attractions uniting the molecules to visible crystal- 
line individuals. The effects of such attractions are even fre- 
quently extended to the position of the crystals to each other. 
Every snow flake represents a system of symmetrically ar- 
ranged numerous hexagonal ice crystals, the hexagonal form 
not only dominating in the single crystals, but being evidently 
noticeable in the whole beautiful arrangement. Common 
salt, when crystallizing from saturated solutions, is seen to 
separate in amphitheatrical square combinations consisting of 
single cubical salt particles. In the single crystals, as well as 
in their congregations, we observed the square predominating 
as the elementary form. : 
Neither in the manifold features of animal and plant life, 
nor in the crystalline formations of mineral matter, are exter- 
nal influences deciding as to the forms to be adopted. Indi- 
viduals of different natural character of different species, grow 
up and become differently shaped, although exposed to the 
same external conditions. A slight transforming influence of 
temperature, light, food and contact cannot be denied, but the 
