DIGESTION 



331 



Bacterial action is not essential to digestion. By taking 

 embryo guinea-pigs at full time from the uterus and keeping 

 them with aseptic precautions, it has been shown that the 

 absence of micro-organisms from the intestine does not inter- 

 fere with their nutrition. 



E. Fate of the Digestive Secretions. 



1. Water. — Although it is impossible to state accurately 

 the averaCTe amount of the various digestive secretions 



Mouth. 



Stomach. 



Small 

 Intestine. 



Lakge 



Intestine. 



AmYLOLYTIC ^OTEOLYTIC LiPOLYTiC 



I 1 1 1 Alkaline mmm/KcvD Putrefactive 



Fig. 155. — A Sjmopsis of the Conditions and Processes in tiie Different 

 Divisions of the Alimentary Canal in the pig and in man. The nature 

 of the control — nervous or chemical — is indicated in the top line. 



poured inio the alimentary canal each day, it must be very 

 considerable, probably more than one-half of the whole 

 volume of the blood. Only a small amount of this is 

 given ofY in the f«ces, and hence the greater part must be 

 re-absorbed. There is thus a constant circulation between 

 the blood and the alimentary canal, or what may be called 

 an entero-haemal circulation. One portion of this, the entero- 

 hepatic, is particularly important. The blood-vessels of the 

 intestine pass to tlie liver, and many substances, wlien 

 absorbed into the blood-stream, are as^ain excreted in the 

 bile and are thus prevented from reaching the general 



