NATURAL HISTORY OF ORGANIZED BODIES 289 



accordincr as the diameter of the vessel is increased or diminished. This m(!thod 

 is susceptible of a great number of applications ; it enables us to show that all 

 the vascular organs undergo, at each sanguineous discharge from the heart, a 

 distension followed by contraction, similar to that presented, in a higher degree, 

 by the erectile tissues. But this mode of examination is not new ; there may bo 

 seen in the works of Swammerdam the description of an apparatus very analo- 

 gous to the one in question, and destined to determine whether a muscle in con- 

 tracting undergoes a change of volume. 



Of all the phenomena which characterize life, movement is the most import- 

 ant ; it may be said, indeed, that in general it is movement which gives their 

 distinctive character to all the functions; now, it is under this aspect that the 

 phenomena of animal life can be analyzed at present with the most admirable 

 precision in the three correlative elements of duration, extent, and /orce. We are 

 but little capable of appreciating duration with exactness, especially that which 

 is very short, and we generally consider as instantaneous such phenomena as 

 occupy a space of time shorter than the half or quarter of a second. For the 

 same reason we assume the synchronism of two acts which follow one another at 

 a short interval. But chronometry has made so much progress of late that Ave 

 can now measure the shortest durations, thardvs to the apparatus employed by 

 the physicists. The velocity of projectiles, of light, of electricity, is readily 

 reduced to measurement, and nothing prevents the application in general of the 

 same methods to the still shorter durations of physiological acts. The extent of 

 a movement is susceptible of very exact a})prcciation, i)rovided the movement fur- 

 nishes a trace which may ])e afterwards submitted to the estimates of micron)etry. 

 The idea o^ foirc has recently undergone an important modification; it has been 

 reduced to that of kdor accomplislied, and is referable hencclbrth to a determinate 

 standard, the kilogratnmetre and its divisions. We find ourselves therefore in 

 possession of accurate terms of comparison, and should eliminate in future every 

 vague expression relative to movement. We should characterize it in every case 

 according to its duration referred to the second of time, its extent in terms of the 

 metre or its fraction, its force as expressed in kilogrammetres. Perhaps a still more 

 complete conception is that which further characterizes a movement by its form ; 

 that is to say, which takes account of the different phases of the movement, and 

 no longer onh^ of its commencement and end, its maximum and minimum, but 

 which determines all the intermediate states. Such is the result obtained by the 

 (jraylnc nietltod, to which 1 shall have occasion elsewhere to call attention, as 

 furnishing of itself the solution of a great number of problems of the highest 

 imi)ortance. 



Movement, before being executed, is, so to say, ])otentially contained in certain 

 causes which produce it : weUjht, elasticity/, the pressure of a liquid, the tension 

 of a gas. W^e now know how to a})preciate these forces, which may be called 

 virtual. It is statics which measures them, and introduces into their measure- 

 ment that rigoroiTs exactness which tends at present to become general. The 

 application of the ynanometer to the valuation of the pressure of the blood, of the 

 thoracic aspiration, t)f the force with which the glandular reservou's contract, is a 

 further step in the progress of our epoch. 



If I have here given but a rajjid and incomplete enumeration of all these exact 

 processes and their apjn-opriate apparatus, it is because the occasion will here- 

 after present itself, in my collegiate course, of describing them more completely, 

 and of more fully exemplifying their value. I have aimed to show in the first 

 place the resources which we have at oin- disposal, and to prove especially that 

 it is by drawing more closely its relations with the other sciences, that biology 

 has become progressive and will continue to progress. Now that we are })ro- 

 vided with new means for atteuqiting the solution of the problems of life, we 

 may resume the researches in which our predecessors have been foiled. A 

 subject which might be supposed to be exhausted becomes once more a fertile 

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