2 Comparative Physiology and Psychology. ([January, 
H. C. Sorby! estimated the number of molecules in p% inch 
sphere of albuminous substances to be 
PE aa © oo 5 sg ws ca os ob ee es 10,000,000,000,000 
Water. sircss Se ce bs ees a a eevee 520,000,000,000,000 
Water in molecular combination. .......-..eeeeeee- 5.30,000,000,000,000 
and claims that we are as far from seeing the ultimate constitu- 
tion of organic matter with our highest and best powers as the 
naked eye is from seeing the smallest objects which they now 
reveal to us, and that there seems no hope that we may ever see 
them, for light is too coarse. 
This is a limit to our sense appreciation of the subject. Reason 
enables us to make safe guesses beyond the senses, but having 
them for a guide and acknowledging that science does not require 
final but effective causes. 
The “selection” of food which is suited to the Amceba be- 
comes “selection” or mere chemical attraction depending upon 
how you look at it. For instance, let the assimilable pabulum 
consist of molecules for which the protoplasm has affinities or 
attractions, the Amceba will not only be drawn to it locomotori- 
ally, but will fuse about it. As it is drawn into and becomes part 
of its tissue, there is undeniable chemical union, the inert result- 
ing matter is left behind or excreted in the movements. The 
inert matter not only does not attract the animal, but even its 
passing by or over it the assimilative motions are not provoked. 
There could be an endless wrangle over the nature of this act of 
the protozoon, for it involves the most weighty considerations in 
all life. There is much to be said on all sides, but the moment 
the acknowledgment is made that chemical affinity and other 
physical influence is not the so-called will power of the Amceba, 
that moment there is an end to investigation. Admitting that these 
natural causes exert entire control of the protozoon, and forthwith 
the postulate proves its correctness in exact proportion to the 
correctness of the logical methods used in reasoning therefrom. 
Much of the perplexity into which the student has been thrown 
by regarding these movements has arisen from want of considera- 
tion of the composition of resultants of attraction from many 
points in the medium or environment due to light, heat, eddies, 
vortices, disseminated invisible attracting points, the assimilative 
process itself changing the conditions of attraction, as in plethora ; 
1 Presidential address Royal Micros. Soc., Feb, 2, 1876, 
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