212 



must be specific and undivided ; the several objects and their con- 

 nexions must never be lost sight of; in the conduct of it there must 

 not be one superfluous design, and in the detail of its results not one 

 superfluous sentence. This is a project, I fear, for the next age : we 

 must for the present, at least in this place, be content to proceed 

 more loosely, without however wholly losing sight of these indica- 

 tions for an analysis. 



3. Lacteal chyle being poured into the sanguiferous system, of 

 course becomes red by its mixture with blood ; but a source of its 

 colorification is necessary, 1st, because the present red blood is 

 changed, or other blood substituted for it from the lacteal fluid, in 

 the lapse of time; and, 2nd, because, although a white fluid may 

 have its colour changed by mixture with a red one, this mode could 

 not obtain before the red fluid was formed, viz. in the first periods 

 of the ovum ; or, as best exemplified in the stages of incubation. 

 Some source of the colour therefore is necessary. 



4. The change of colour is the most obvious one which chyle 

 undergoes: perhaps in real utility it might be subordinate, or 

 probably altogether unimportant. Whether this change is only a 

 concomitant with others, and what those others are, can be deter- 

 mined only by our comparative analysis. The seats of those other 

 changes are to be sought after when the changes can be specified ; 

 for the present, we may take the obvious one of colour, as a clue Jo 

 the investigation of the associated changes which we have supposed. 



5. If it is inquired generally what is the seat of the conversion 

 pf chyle into blood? it must be replied, as generally, the seat of it 

 is in (he vascular system, where it is observed to occur; but a more 

 particular question would require us to specify in what blood-vessels, 

 or in what structure of their distribution, or is the faculty of the 

 conversion common to all? 



6. The general opinion seems to tie that arterial blood is made 

 in the lungs; that venous blood is a product connected with a 

 function either of the arterial capillary terminations, or of the 

 minute origin of the veins. 



