LECTURE XXII. 



THE FUNCTIONS OF THE DIGESTIVE ORGANS. 



II. 



FROM the stomach the food reaches the duodenum, and undergoes an 

 energetic digestion. Here, as we have already repeatedly stated, the food- 

 stuffs which in their composition are complex and unlike, as well as entirely 

 unsuited for direct absorption by the tissues, are to a greater or less extent 

 broken down into their simpler components. Thus complicated carbo- 

 hydrates are transformed into the simplest sugar, the albumins into 

 amino acids and polypeptides, and the fats eventually into fatty acids 

 and glycerbl. From these materials the body is able to construct the 

 components of its tissues. Digestion serves not only to make the sub- 

 stances suitable for absorption, but, above all, for assimilation. 



By means of this breaking down of the foodstuffs, the animal organism 

 makes the cells of its tissues to a large extent independent of the nature of 

 its food. It is to the cells a matter of indifference whether the food is of 

 animal or vegetable origin; they will in all cases receive the same carbo- 

 hydrates, the same fats and proteins from the blood. We may state in 

 advance that evidently the walls of the intestine themselves play an 

 important part in effecting the transformation of the separate foodstuffs. 

 Within them takes place, according to our present knowledge, the building 

 up of albumin and fat from the more simple components. Absorption 

 takes place without doubt in proportion as this synthesis is accomplished. 

 This fact makes it difficult to trace the exact relations of the foodstuffs 

 to the intestine. Our knowledge ceases essentially with the taking up of 

 the food by it. It might be thought that some idea of the complicated 

 processes taking place in the intestine could be gained by causing, with 

 suitable methods, an accumulation of the decomposition and synthetical 

 products, e.g., in the examination of a surviving intestine. Up to the 

 present time, however, such experiments have failed to give satisfactory 

 results. The absorption of fats and their synthesis from the simple com- 

 pounds has alone been followed to a certain extent by means of the micro- 

 scope. With the proteins the relations are far more complicated. The 

 walls of the intestine themselves consist chiefly of albumin. It is hard 

 to tell what is new and what was originally present. As long as we are 

 unable to differentiate sharply between the different albumins, there is 

 practically no prospect of our being able to get direct proofs by means of 



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