( 706 ) 
the chemical cycle may be slight at first and by approximation all 
the considerations remain of force for this short period, also for a 
part of a reflex-apparatus, but after a longer period atrophy neces- 
sarily sets in. As soon, however, as the chemical cycle is no longer 
complete, the reflex-apparatus will be in a changed state after each 
stimulation. This interrupts the regularity of the phenomena. 
Some botanists have tried to introduce into botanical physiology 
the notion of a reflex-apparatus built up by a concatenation of celis. 
There is here, however, no question of a differentiated reflex-appa- 
ratus, and a great many investigations have proved, that the same 
cell which receives the stimulus serves at the same time as trans- 
former. Evidently the whole cycle of metabolism takes place in 
a single cell. It is therefore more accurate to consider the cell asa 
physiological unit for plants and probably also for the lowest animals. 
In a second paper I hope to discuss the law according to which 
the transition of the system of the products of assimilation to the 
products of dissimilation takes place and the results which ensue 
from this for the reflex-apparatus. 
Physiology. — “The principle of entropy in physiology.” By 
Dr. J. W. LANGELAAN. 2rd part (Communicated by Prof. 
T, PLACE). 
In this paper I shall try to discuss the law according to which 
the system of the products of assimilation passes over into that of 
the products of dissimilation. Our knowledge of the nature of these 
two systems is very limited. We scarcely know, which are the prin- 
cipal components originally present and which are the later appea- 
ring. The equations of condition existing between these components, 
are also only partly known to us as regards their form and their 
number. The number of independent variable components is therefore 
not known to us. The only thing we kaow with certainty is that 
we have to deal with condensed systems. 
When the application of thermodynamics in its simplest form is 
correct, the same law will hold true for the transition of the system of 
the senior of assimilation to that of the products of dissimilation 
as that according to which two condensed systems pass into one another. 
Supported by a considerable experimental material VAN ’t Horr 
has applied here the following formula ') : 
1) Van *r Horr, Vorlesungen ltes Heft 1898 p, 175. 
