48 MEMOIR OF BARON HALLER. 



transparent. We see not the wind. Too small and 

 feeble to produce any effect upon the surrounding 

 fluid, the heart has appeared motionless, as it pre- 

 Yiously had appeared to he wanting. This con- 

 sideration should anticipate the conclusion we are 

 prone to draw, that an animal lives, or does not 

 live, or that it begins to live at this or that moment 

 which we choose to fix : we recognize life only by 

 motion, and motion is apparent only by a certain 

 gize and opacity. 



But whence this opacity, and by what shades 

 do colours appear ? There is but one step between 

 mucous transparency and whiteness : a little more 

 liquid confers transparency on white bodies, and a 

 little less deprives them of it. Paper is white, and 

 o is pounded glass, yet both become transparent 

 when soaked in water or oil : remove these liquids, 

 and they again become white. Even the fat of 

 living animals is transparent; a slight dissipation 

 of its fluid parts, and its cooling by air, make it 

 white. 



White then is the first colour of the animal, as 

 transparency is its first condition. This is true of 

 all the quadrupeds upon whom I have made expe- 

 riments, and these have been very numerous; the 

 same is true respecting birds. The colours are pro- 

 duced by the power of the heart dilating the ves- 

 sels, and so allowing them to transmit the coloured 

 particles, which, according to the principles pointed 

 out by Newton, are always larger than diaphanous 

 particles. In the chick we find occurring the yellow, 



