

PHYSIOLOGY. 191 



have hardly mentioned any other means for this union of oil, 

 but the application of viscid fluids ; but these can occasion only 

 a diffusion, and some means of mixture must necessarily be sup- 

 posed. What these, however, are, we do not certainly know. 

 They do not produce their effect in the first passages ; for in 

 the chyle, till it enters the subclavian vein, the oil appears to be 

 only in a diffused state, and probably the perfect mixture is only 

 made in the passage through the lungs. 



CCXLI. It may be proper here to take notice of another 

 matter which constantly enters into the mixture of animal fluids. 

 This is air, which, by different means, can be extracted in con- 

 siderable quantity from every kind of animal matter. What is 

 properly the origin of this, when and where it is insinuated into 

 the animal fluids, and by what means it is either fixed in these 

 or loosened from them, are all questions not yet resolved, but 

 perhaps necessary to be resolved, before we can speak with any 

 confidence of the changes which the animal fluids undergo in 

 different parts of the system. We can observe, in the mean 

 time, that a quantity of air is always present in the chyle in a 

 very loose state ; that it becomes more fixed in the mass of 

 blood after this has passed through the lungs ; and that again, 

 in the different secreted fluids, the air appears to be in some of 

 them still fixed, and in others much more loose ; and it is pro- 

 bable, that all this has a particular relation to the production 

 and properties of the different fluids of animals. 



CCXLII. We have now followed the course of the aliments, 

 so far as we can consider them as any ways in a separate state ; 

 but we do not perceive, that, in any part of this course, the 

 proper animal fluids are entirely formed ; and it is very justly 

 supposed, that the proper mixture or assimilation is not finished 

 till the chyle, mixed with the mass of blood, has undergone the 

 action of the lungs, through the vessels of which it must almost 

 immediately pass after entering the subclavian vein, and seem- 

 ingly before it is applied to any of the purposes of the animal 

 economy. 



CCXLI II. What change the fluids undergo in passing 

 through the lungs, or by what means the supposed changes are 

 produced, after all that has been said, seems still to be very lit- 

 tle known. 



