Page:The New International Encyclopædia 1st ed. v. 06.djvu/290

DIGESTION. 2i6 DIGESTION. ical ooiiipositioii. the collective solid constituents ranpng from 1.5 to 2.3 per cent., the organic matters from 0.9 to 1.6, and the mineral matters from 0.ti2 to 0.75. The most nlnuuhuil and iiii|iortaMl of the solid con.stituent.s is a peculiar substance termed piin- crcolim, or pancreatic diastase or ferment, in combination with soda, to «hich this lluid owes its principal chemical and ])h_vsiol();;ical proj)- erties. Calculating from the quantity of pan- creatic juice secreted by dogs of known weight, we may infer that a man weighing 140 pounds secretes daily about 10 ounces of this lluid. One of the chief uses of the pancreatic juice in relation to digestion is to convert into sugar the amylaoeous or starchy matters which have escaped the acticm of the saliva and have |)asscd unchanged into the duodenum. It possesses this property in a far higher degree than the saliva, and, as might be expected in reference to this use, the pancreas is found to be much more de- veloped in herbivorous than in carnivorous ani- mals. Bernard, the representative of the modern school of physiology in France, claims for thi.5 llui<l another important function — he believes that he has proved that it is solely by the action fif this .secretion that the fat is reduced to a con- dition in which it can be absorbed and digested: that is to say, that it is decomposed intc glycerin and a fatty acid. (See Fat.s. ) This view has, however, not been generally accepted, and it seems probable that although the change de- scribed by Bernard takes place when fat and pancreatic juice are simply mixed together in a test tube, it does not actiially take place in the intestine, the acid gastric juice probably acting as an interfering agent. An attempt has lately been tuade by Corvisart and ileissner to prove that, like the gastric juice, this lluid can dissolve albuminous matters : but this view cannot be sub- stantiated. Considering the large quantity of pancreatic fluid which is yielded in twenty-four hours, Schmidt, who has made the digestive juices the subject of his special study, is of opin- ion that the function of this fluid is not so much to promote the conversion of starch into sugar as for the purpose of diluting the chyme, and for reconverting the soda (which in the pancreas has been separated from the chlorine of the chloride of sodium, and has combined with the pancrea- tine) into chloride of sodium. He shows, from numerical calculations, that more than half of the chloride of sodium existing in the blood which circulates through the pancreas is broken up into hydrochloric acid and stHla. of which the former is separated by the gastric glands, while the latter unites with the pancreatine. ^Meeting again in the duodenum, the hydrochliiric acid and the soda, retinit^ and re-form chloride of sodium, which is again absorbed and n'enters the circu- lation. This is perhaps one of the most singtdar decompositions and reunions occurring in the animal body. Of the last of the fluids poured into the in- testine and cooperating in the digestive process, the inlrslinal juice, we know comparatively lit- tle. It is the aggregate secreticm of the vari- ous glands which we have described as occurring in the walls of the small intestine. It is a color- less, or sometimes yellowish, ropy, viscid fluid, which is invariably alkaline. We are not aware of any special characteristic constituent in it, such as occurs in the other chylopoietic fluids. Its daily quantity is probably nine or ten ounces. It seems to unite in itself the leading pro|)ertics of the pancreatic and gastric juices; that is to say, it resembles the former in converting starch into sugar, and the latter in dissolving flesh and other albuminous bodies. We shall conclude this part of the subject w ith a few remarks on the clieniical composition of the contents of the small intestine. On laying open the gut we usually find a semi-solid ad- mixtire of imperfectly iligcstcil and indigestible substances, and of the constituents of the diges- tive fluids in a more or less changed condition. The reaction of this mass varies in dilTerent parts of the canal, and in some measure with the na- ture of the food. Thus, the contents of the stom- ach always redden litmus paper, whatever kind of food has been taken; the duodenal contents are also always acid, but in a far less intense degree; in the jejunum we meet with only a faint acid re- action, which altogether disappears in the ileum; while in the c;ecum, and sometimes in the lower part of the ileum, an alkaline reaction occurs. .fter a purely animal diet the acid reaction dis- appears shortly below the duodenum : while, after the sole use of vegetable food, it may souu'tinies be traced even to the ciccum. .s a general rule the contents of the larire intestine are alkaline. In consequence of the rajiid absorption that goes on along the intestinal surface, we meet with a comparatively small amount of soluble matters in these contents. Among these soluble matters we often find glucose (or grape-sugar), which seems to owe its origin to the raetamor- jihosis of starch, and not to sugar having been present in the food ; for a f ter sac- charinc food has been taken we rarely meet with it in any quan- tity in the small in- testine, its absorption taking place with great rapidity. In the alcoholic extract of these contents we can almost always find evidence of the presence of biliary constituents. In the duo<lenum, and for a little way beyond it, we find glycocholic and tauiocholic acid: de- scending a little far- ther they rapidly dliii- iiiisli. till we find the products of tludr ilis- intcgration; while in ili>s of tin- vnlvc sciiarntlnjr the large intestine ll'eBinnll from (li..l,.rK.- lnt«.. ,..., - ., tine; >f. tlH' vt^rmiforni npix'n- little more than a dix „( iiiPcmiiiM. trace of these prod- ucts can be detected. These chemical tibserva- tions confirm the experiments of Schmidt, which show that nearly half the bile which is poured into the duodenum is decomposed before it reaches the middle of the small intestine. (7) We have now arrived at the seventh stage of the digestive process — that of (Irfrralinii. The line of demarcation between the small and large intestine is very- obvious, and by the peculiar ar- rangement of the ileoca'cal valve (see Fig. 10) ri(i. 10. rn><iiiii liillnta'd. ilrlwl. and opened to show tlio arrangw- inent of the valve. .I. termination of the llnim: h, uKe4>ndlnfr rolon; r. ra>euin; f/. n transverse const ruction projrt'tlnt; Into the fir«Mini; e f.