BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 447 



iugs lias rendered it familiar to all students. Both writers mean by 

 the word energy, not the " capacity of doing work," but simply activity^ 

 using it in its old-fashioned meaning, that of the Greek word from 

 which it is derived. With the qualification '' specific," it serves, per- 

 haps, better than any other expression to indicate the way in which 

 adaptation manifests itself. In this more extended sense the " specific 

 energy" of a part or organ — whether that part be a secreting cell, a 

 motor cell of the brain or spinal cord, or one of the photogenous cells 

 which produce the light of the glowworm, or the protoplasmic plate 

 which generates the discharge of the torpedo— is simply the special 

 action which it normaUij performs, its norma or rule of action being in 

 each instance the interest of the organhm as a whole of wdiich it forms 

 part, and the exciting cause some influence outside of the excited struc- 

 ture, technically called a stimulus. It thus stands for a characteristic 

 of living structures which seems to be universal. The apparent excep- 

 tions are to be found in those bodily activities which, following Bichat, 

 we call vegetative, because they go on, so to speak, as a matter of 

 course; but the more closely we look into them the more does it appear 

 that they form no exception to the general rule, that every link in the 

 chain of living action, however uniform that action may be, is a response 

 to an antecedent influence. Nor can it well be doubted that, as every 

 living cell or tissue is called upon to act in the interest of the whole, 

 the organism must be ca]>able of influencing every part so as to regu- 

 late its acfion. For, although there are some instances in which the 

 channels of this influence are as yet unknown, the tendency of recent 

 investigations has been to diminish the number of such instances. In 

 general there is no difliculty in determining both the nature of the cen- 

 tral influence exercised and the relation between it and the normal 

 function. It may help to illustrate this relation to refer to the express- 

 ive word AndosHug, by which it has for many years been designated by 

 German writers. This word stands for the performance of function by 

 the "letting oft" of "specific energies." Carrying out the notion of 

 "letting oft" as expressing the link between action and reaction, we 

 might compare the whole process to the mode of working to a repeating 

 clock (or other similar mechanism), in which case the pressure of the 

 finger on the button would rei»resent the external influence or stimulus, 

 the striking of the clock, the normal reaction. And now may I ask 

 you to consider in detail one or two illustrations of physiological 

 reaction — of the letting off of specif c energg '! 



The repeater may serve as a good example, inasmuch as it is, in bio- 

 logical language, a highly differentiated structure, to which a single 

 function is assigned. So also in the living organism, we find the best 

 examples of specific energy where JMiiller found them, namely, in the 

 most difterentiated, or, as we are apt to call them, the highest structures. 

 The retina, with the part of the brain which belongs to it, together con- 

 stitute such a structure, and will aflord us therefore the illustration we 



