448 HISTORY OF PHYSIOLOGY. 



lose most of the chances of ulterior progress ; for 

 though it may be, that our conceptions of the 

 nature of organic life are not yet sufficiently precise 

 and steady to become the guides to positive induc- 

 tive truths, the only way in which these peculiar 

 physiological ideas can be made more distinct and 

 precise, and thus brought more nearly into a scien- 

 tific form, is by this struggle with our ignorance or 

 imperfect 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. 



That the food is received into the stomach, there 

 undergoes a change of its consistence, and is then 

 propelled along the intestines, are obvious facts in 

 the animal economy. But a discovery made in 

 the course of the seventeenth century brought into 

 clearer light the sequel of this series of processes, 

 and its connexion with other functions. In the year 

 1622, Asellius or Aselli 1 discovered certain minute 

 vessels, termed lacteals, which absorb a white liquid 

 (the chyle) from the bowels, and pour it into the 

 blood. These vessels had, in fact, been discovered 



1 Mayo, Physiology, p. 156. 



