i52 HISTORY OF PHYSIOLOGY. 



CHAPTER III. 



DISCOVERY OF THE MOTION OF THE CHYLE, AND CONSEQUENT 



SPECULATIONS. 



Sect. 1. The Discovery of the Motion of the Chyle. 



IT may have been observed in the previous course of this History of 

 the Sciences, that the discoveries in each science have a peculiar 

 physiognomy : something of a common type may be traced in the pro- 

 gress of each of the theories belonging to the same department of know- 

 ledge. We may notice something of this common form in the various 

 branches of physiological speculation. In most, or all of them, we 

 have, as we have noticed the case to be with respect to the circu- 

 lation of the blood, clear and certain discoveries of mechanical and 

 chemical processes, succeeded by speculations far more obscure, doubtful, 

 and vague, respecting the relation of these changes to the laws of life. 

 This feature in the history of physiology may be further instanced, (it 

 shall be done very briefly), in one or two other cases. And we may 

 observe, that the lesson which we are to collect from this narrative, is 

 by no means that we are to confine ourselves to the positive discovery, 

 and reject all the less clear and certain speculations. To do this, would 

 be to lose most of the chances of ulterior progress ; for though it may 

 be, that our conceptionmrf the nature of organic life are not yet suffi- 

 ciently precise and steady to become the guides to positive inductive 

 truths, still the only way in which these peculiar physiological ideas 

 can be made more distinct and precise, and thus brought more nearly 

 into a scientific form, is by this struggle with our ignorance or imper- 

 fect knowledge. This is the lesson we have learnt from the history of 

 physical astronomy and other sciences. We must strive to refer facts 

 which are known and understood, to higher principles, of which we 

 cannot doubt the existence, and of which, in some degree, we can see 

 the place ; however dim and shadowy may be the glimpses we have 

 hitherto been able to obtain of their forms. We may often fail in 

 such attempts, but without the attempt we can never succeed. 



