CHAPTER LIX 



BACTERIAL DIGESTION IN THE INTESTINE 



On an average diet, in twenty-four hours the feces of man weigh 

 about 100 grams, or after drying, about 20 grams. About one-fourth of 

 the dry matter consists of the bodies of bacteria. If plated out by the 

 ordinary bacteriologic methods, however, it will be found that only a 

 small proportion of these bacteria are living. The greater number have 

 been destroyed, probably by the action of the mucin in the large intes- 

 tine. The nitrogen content of the feces amounts to about 1.5 grams a 

 day, of which about one-half is bacterial nitrogen. If the diet contains 

 large quantities of cellulose material, as in green vegetable food and 

 fruit, the mass of feces as well as the bacterial content may be consid- 

 erably greater. 



The foregoing facts indicate that very extensive bacteriologic proc- 

 esses must be going on all the time in the intestinal contents, and the 

 question arises as to whether such action is beneficial or otherwise to the 

 animal economy. To answer this question interesting observations have 

 been made on the growth and well-being of animals excised from the 

 uterus under strictly sterile conditions and maintained thereafter on 

 sterile food. Such observations made on guinea pigs have shown that 

 the animals thrive and grow perfectly for a considerable time. Experi- 

 ments carried out on chicks have not, however, yielded similar results. 

 Chicks hatched out from the egg under strictly sterile conditions and 

 then fed on sterile grain, do not thrive, but do so if with the grain is 

 mixed a certain amount of fowl excrement. These experiments, appar- 

 ently contradictory in their results, show that for certain groups of 

 animals bacteria are required, but not for others. 



The difference is probably dependent on the nature of the foods. It 

 will be remembered that the size of the large intestine varies consider- 

 ably according to the nature of the diet (see page 497). Animals taking 

 great quantities of cellulose foodstuffs have very large ceca and very 

 long large intestines; whereas those which, like the cat, live practically 

 entirely on cellulose-free food, have a rudimentary large intestine. The 

 size of the lower intestine is obviously dependent on the presence or 

 absence of cellulose in the food. It will be remembered also that the 

 forward movement of the contents of the large intestine is very slow ; 

 indeed, special provision is made, by the presence of the so-called anti- 

 peristaltic wave, to delay its movement. This suggests that an important 



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