FUNCTIONS OF THE LARGE INTESTINE 815 



very inadequate. In some cases after the introduction of large 

 enemata into the large intestine a certain amount may escape back- 

 wards into the ilemn and may there undergo absorption. The 

 isolated large intestine of man is able to absorb only about six grammes 

 of dextrose per hour and about 80 c.c. of water. If egg albumin 

 or caseinogen solutions be introduced by the rectum no absorption 

 can be detected after several hours. In observations extending over 

 a considerable time some disappearance has been observed of proteins 

 and emulsified fats, as well as of boiled starch. This was due, how- 

 ever, to the action of bacteria on these substances, and was probably 

 of very little value for the nourishment of the individual. Feeding 

 by nutrient enemata is thus merely a method of slow starvation. 

 If it is employed it should be limited to administration of water, 

 salines, or solutions of glucose. 



The chief value of the large intestine in carnivora and in civilised 

 man would seem to be as an excretory organ, since it plays an impor- 

 tant part in the excretion of lime, magnesium, iron, and phosphates. 

 Lime salts are excreted partly with the faeces, partly in the urine. 

 The path taken by the lime under different conditions varies with 

 the character of the other constituents of the food. If phosphates 

 are present in large quantities the greater part of the lime will be 

 excreted by the large intestine and escape with the faeces as insoluble 

 calcium phosphate. If acids be administered, such as hydrochloric 

 acid, the amount of lime in the urine will increase, that in the faeces 

 will diminish. Thus in herbivora normally only about 3 to 6 per 

 cent, of the lime is excreted with the urine, whereas in carnivora 

 with an acid urine the proportion leaving the body by this channel 

 rises to 27 per cent. The excretion of magnesium is determined by very 

 similar conditions. Its phosphates are somewhat more soluble than 

 those of lime. Thus in man about 50 per cent, of the magnesium leaving 

 the body is contained in the urine, whereas the amount of lime 

 contained in the faeces in man is ten to twenty times as much as that 

 contained in the urine. It must be remembered that the whole of 

 this difference is not due to excretion of lime into the gut, since a 

 certain proportion of this substance may be precipitated as an 

 insoluble phosphate or carbonate in the upper part of the small 

 intestine and pass through the gut without undergoing absorption. 



The absorption of iron takes place in the duodenum and upper 

 part of the jejunum. Only 1 or 2 milligrammes appear in the urine, 

 all the rest being excreted in the large gut and appearing in the 

 faeces, chiefly as sulphide of iron. 



Of the acid radicals phosphates may pass out either with the urine or 

 with the faeces, the exact path taken being determined by the relative 

 amount of calcium and alkaline metals present in the food. If there 



