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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 disco- 

 veries in each science have a peculiar physiognomy: 

 something of a common type may be traced in the 

 progress of each of the theories . belonging to the 

 same department of knowledge. 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 circulation 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 



