NUTRITION PROPER. 



32S 



and fats are transparent, but broken up into microscopic 

 globules they are also white. Now, what is called an 

 emulsion consists of millions of microscopic globules of 

 oil swimming in a transparent liquid, but, in order that 

 the globules do not run together and unite, the liquid 

 must be viscid. 



Experiment. — Take a small bottle, fill it partly with 

 a viscid liquid like gum water or mucus, and then pour 

 in a little oil of some kind, as turpentine or sweet oil. 

 We see them as two equally transparent layers one atop 

 the other. Now, putting the thumb on the mouth of 

 the bottle, shake it violently." The result is an intensely 

 white fluid, which, examined by microscope, shows noth- 

 ing but transparent globules floating in a transparent 

 liquid. This is an emulsion. Milk is also an emulsion, 

 and its whiteness is due to the same cause. Chyle is an 

 emulsion, and its whiteness is due to the presence of 

 microscopic fat globules. If there be no fat in the food, 

 the chyle will be transparent. In the process of diges- 

 tion the fats and oils are broken up by the constant 

 pressing and kneading ac- 

 tion of the intestines in the 

 presence of a viscid liquid. 



Absorption . — The 

 three kinds of food are 

 now all become absorb- 

 able. The starches have 

 become sugars, the albu- 

 minoids peptones, and the 

 fats emulsions. The food 

 is now ready for absorp- 

 tion. But for rapid ab- 

 sorption we must have a 

 large surface. This con- 

 dition is supplied partly 



Fig. 207. — Interior of the intestines, 

 showing the valvule conniventes. 



