( 700 j 
Ist. The temperature must be constant throughout the whole 
system. This is the necessary and sufficient condition for the thermal 
equilibrium. 
2nd. The pressure must be constant throughout the whole system. 
This condition is necessary and sufficient for the mechanical equilibrium. 
3d, The thermodynamic potential must be constant for every 
independent variable component of the system throughout the whole 
system. This is the characteristic condition for the chemical equilibrium. 
Equilibrium can only exist, when these three conditions are simul- 
taneously satisfied. The applicability of the two first conditions of 
equilibrium to physiological systems is not open to doubt, the appli- 
cation, however, of the third condition of equilibrium forms a neces- 
sary hypothesis for the application of the more special results of 
thermodynamics to physiological systems. 
In order to apply the results of thermodynamics, we imagine a 
reflex-apparatus, which is thermally, meehanically and chemically 
isolated. The reflex apparatus itself is thought as consisting of a 
generally peripherically situated) receptive-apparatus going over in 
or connected with an afferent nerve, which is connected in the central 
organ with the cellbody of an efferent nerve. This efferent nerve 
carries as endorgan a transformer. 
This transformer can be a muscle, in which case it chiefly 
transforms potential energy of the chemical system into mechanical 
work and heat. The nature of the transformer and the external 
circumstances determine how the distribution in the two forms of 
energy will take place. If the transformer is a gland, a chemical 
system is transformed into another and into heat. Here it is chiefly 
the nature of the transformer which determines the final result. If 
wel apply the name of transformer to the muscle and to the gland, 
we do so because in these organs the transformation is most prepon- 
derant. In reality the whole reflex-apparatus transforms energy, but 
the part which the before-mentioned organs take in it is so prevail- 
ing, that no appreciable fault is made when we neglect the quan- 
tities of energy transformed in the rest of the reflex-apparatus. If 
the receptive-apparatus is a large senseorgan this neglection is no 
longer admissible. 
In this reflex-apparatus we imagine two chemical systems in 
equilibrium. According to [ring !) one system may be called the 
system of the products of asssimilation, the second that of the products 
') HEerinG, Lotos, Neue Folge, 1889 Bd. IX p. 35, 
