1890.] Study of Natural and Artificial Digestions. 193 



digestive fluid minus the digestive ferment. This parchment dialyser 

 is finally kept in constant up and down motion by means of an 

 appropriate motor, and its contents are thus continuously mixed by 

 the almost "peristaltic" waves which pass over the walls of the 

 tube during its motion. In this way it becomes possible to take 

 advantage of the diffusibility of the digestive products, and effect 

 their more or less rapid removal during any given digestion. It 

 will be further seen that the diffused products can be collected, so 

 that there is no loss of material during the digestion. Moreover, the 

 rate of removal of the products can, within certain limits, be modified 

 by the frequency of changing the fluid into which their diffusive 

 removal takes place. It has not as yet been found possible to supply 

 the third factor in a normal digestion, viz., the continuous addition 

 of fresh digestive ferment. Although the above apparatus is very 

 efficient, as compared with the vessels in which artificial digestions 

 are usually carried on, it falls far behind the natural, and chiefly for 

 two reasons. In the first place, the removal of digestive products is 

 dependent solely and entirely upon their diffusibility, whereas in the 

 alimentary canal there is now no doubt that they are largely removed 

 by the specific activity of the epithelial cells. In the next place, the 

 diffusive exit of the products leads to an influx of fluid into the 

 dialyser, which, by diluting the ferment solution, is detrimental to its 

 continued initial activity. Notwithstanding these shortcomings, the 

 differences in the rate and completeness of a digestion carried on in 

 this apparatus, as compared with those of one carried on under other- 

 wise similar conditions in a flask, are very marked, and indicate that 

 its efficiency is not inconsiderable. 



I may now describe the experiments I have made, the results I have 

 obtained, and the conclusions which may be drawn from them. 



I. — The Salivary Digestion of Starch. 



The information we possess indicates that in the alimentary canal 

 starch is completely converted into sugar before absorption. When, 

 on the other hand, starch is digested artificially with either saliva or 

 pancreatic ferment, the conversion into sugar is never anything other 

 than far from complete, and a bye-product, dextrin, is always obtained 

 in varying but large amounts. My first series of experiments was 

 undertaken with a view to determining the cause of the above 

 difference in the two cases, and to obtain, if possible, an artificial 

 digestion which should be as complete as the natural. It may, 

 perhaps, be said that, inasmuch as in the body starch is digested 

 chiefly, and in some animals entirely, by the pancreatic juice, 

 therefore any deduction from a salivary digestion is not applicable to 

 the pancreatic. But this objection is of no great importance here, 



• Q 2 



