118 II. DIGESTION AND ABSORPTION OF FATS 



Thus, in the case of the adult rat, the small intestine is approximately 2 

 feet long. Although the length of the intestine is not a good index of its 

 surface area, since the latter is likewise a function of the diameter of this 

 organ, it is interesting that this figure more nearly corresponds to body 

 surface than to body weight. The length of the small intestine is about 

 twelve to fifteen times as great in the adult man as it is in the adult rat. 

 On the other hand, the surface area of the body will be about forty times as 

 large, and the body weight two hundred times the magnitude when the 

 values of rat and of man are compared. 



The extremely large value calculated for the area of the small intestine 

 is due to the fact that there are many folds in it, and especially to the fact 

 that the surface is covered with millions of finger-like processes called villi. 

 According to Verzar and McDougall, 554 there are 18 to 40 villi per square 

 millimeter in man, and these have a height of 0.2 to 1.0 mm. The total 

 number of villi is calculated as 5,000,000 in man. In dogs, the villi have 

 an average height of 0.5 to 0.6 mm., a breadth of 0.2 to 0.25 mm. and a sur- 

 face of 0.43 sq. mm. 



The surface area of the small intestine in the rat, without allowing for 

 the area occupied by the villi, has been calculated as 6727 sq. mm. There 

 are, on an average, 6537 villi per square centimeter, which have a surface 

 area of 38,765 sq. mm. This represents a total surface area of 45,486 sq. 

 mm. for the small intestine of the rat; only about one-seventh of the total 

 is contributed by the superficial area of the intestine, while six-sevenths are 

 traced to the area represented by the villi. 



In the case of birds, there is a considerable variation in the type of villi 



Table 16 

 Surface Area of Various Portions of Pigeon's Intestine 



Surface area, sq. mm. Villi 



Segment of Length, Without Villi Length, Breadth, 



intestine mm. villi alone Total mm. mm. 



Duodenum 140 1960 21029 22989 0.84 0.36 



Jejunum 



1st third 200 2400 13708 16108 0.84 0. 18 



2nd third 200 2000 9072 11072 0.42 0.27 



3rd third 200 1800 7387 9187 0.36 0.27 



Ileum 220 880 3564 4444 27 0.45 



Colon 70 490 510 1000 — — 



Total 1030 9530 55,270 64,800 



a Adapted from F. Verz&r and E. J. McDougall, Absorption from the Intestine, Long- 

 mans, Green and Co., London and New York, 1936. Figures for the totals are corrected. 



