204 PHYSIOLOGY. 



the same qualities which it had when it first entered the sub- 

 clavian, and particularly in this state to furnish the milk which 

 is secreted in the breasts of females. There is, however, no 

 proper evidence of the chyle's ever appearing in the blood-ves- 

 sels, and the appearances of it alleged can be otherwise accounted 

 for. The arguments, for the same opinion, which are drawn 

 from the consideration of the secretion of milk, are embarrassed 

 with many difficulties. 



CCLXXI. It is probable that the animal fluid (CCLV. 

 CCLVI.) is in a constant progress, and hardly for a moment 

 stationary, or therefore uniformly the same over the whole of 

 the common mass. Some part of it is that which was last 

 formed, and therefore the nearest to the vegetable matter from 

 which chiefly it was produced ; while another part of it is that 

 which has remained longest in the body, and is therefore the 

 nearest to putrefaction. Between these two there may be se- 

 veral intermediate states, which, however, like the nearest shades 

 of the same colour, are not distinguishable by our senses or ex- 

 periments. 



CCLXXII. Besides the difference of matter arising from 

 the progress of the animal fluid, there have been other matters 

 supposed present in the common mass, and as commonly con- 

 stituent parts of it. Such are a mucous matter, like to the mu- 

 cous matter of vegetables ; and a gelatinous matter, like to that 

 which is extracted by decoction from the solid parts of animals. 

 But there is no evidence of either being formally present in the 

 mass of blood ; and the supposition is founded on mistaken facts 

 and false reasonings. 



CCLXXIII. But it is proper to be observed here, that 

 many extraneous matters may, by different ways, be introduced 

 into the blood-vessels ; and that many of the secreted fluids, 

 sometimes very different from any thing that existed before in 

 the mass of blood, may, by absorption or regurgitation, be 

 again taken into the blood-vessels. But, with regard to all of 

 these, whether extraneous matters or those produced in the 

 body itself, it is probable that hardly any of them enter into 

 the mixture of the animal fluid, and that they are only diffused 

 in the serosity till they can be again thrown out of the blood- 

 vessels by the readiest outlets. The oil of the adipose mem- 



