IOWA ACADEMY OF SCIENCES. 
41 
of ButschlTs alveoli are themselves vesicular, the vesicles 
forming an infinitely graded series down to the extreme 
range of microscopic vision; and, further, that there is the 
most ready interchangeability from one size of vesicle to 
another. All structural features of the cell, when optic- 
ally dissected, are seen to be due to vesicles in a matrix. 
Protoplasm thus embraces two series of structures: (1) 
the continuous substance — the matrix, the active part, 
everywhere continuous throughout the cell, optically uni- 
form; and (2) the inclusions , held by the matrix of contin- 
uous substance, infinitely heterogeneous as to size and con- 
stitution — solid, liquid, or semi-liquid — arranged in a great 
variety of ways. The microscopical appearance of any 
protoplasm is determined by the character and arrange- 
ment of its inclusions. Differences of structure and func- 
tion are due to differences in the inclusions. Vital phe- 
nomena may be conceived to result from the interaction 
between the continuous substance — everywhere uniform, 
and the inclusions — everywhere varied. 
This conception of protoplasm as a microscopical sub- 
stance illumines, as with a flood of light, the phenomena of 
cell-life. We are thereby prepared for an understanding 
of the entrance of matter into the cell: of the translation 
of matter from one point in the cell to another; to grasp 
the basis of the chemical reactions which occur in the cell; 
to realize how the results of irritation spread so readily; 
and to find a physical basis for the unity of the organism. 
II. THE CHEMISTRY OF PROTOPLASM. 
It certainly is significant that the elements composing 
living matter are not scattered at random through the 
natural system, but that they comprise a fairly well- 
defined group, characterized by low atomic weights. The 
extreme lability of protoplasm as a substance is doubtless 
the direct outcome of the instability of the compounds 
which these very elements tend to assume. 
Not less significant is the fact that protoplasm is a 
watery substance, holding certain salts in small quantities. 
