192 



Dr. A. Sheridan Lea. A comparative [Feb. 20, 



February 20, 1890. 



Sir G. GABRIEL STOKES, Bart., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



L " A comparative Study of Natural and Artificial Digestions.'' 

 (Preliminary Account.) By A. Sheridan Lea, Sc.D., Fellow 

 of Gonville and Caius College, Cambridge, University 

 Lecturer in Physiology, Cambridge. Communicated by 

 Professor M. Foster, Sec. R.S. (From the Physiological 

 Laboratory, Cambridge.) Received February 12, 1890. 



When the conditions under which artificial digestions are usually 

 carried on are compared with those under which digestion takes 

 place in the alimentary canal, it is seen at once how imperfect the 

 former are in comparison with the latter. The most important 

 factors present in natural digestion, and wanting in the artificial, are : 

 1. Constant motion and mixing of the digesting mass. 2. Constant 

 removal of the digestive products. 3. Continuous addition of fresh 

 portions of digestive fluid. These factors must determine that natural 

 digestion is more rapid and complete than is the artificial imitation, 

 and my experiments were begun with a view to carrying out artificial 

 digestions under conditions which should supply some at least of 

 those which are usually wanting in such cases, but are always present 

 in the natural process. The apparatus employed may be described as 

 follows : — A stream of water is warmed by passing through a heated 

 copper coil, and allowed to flow through a vertical cylindrical vessel 

 in which is concentrically immersed a smaller cylindrical glass vessel 

 some 2 feet high and 4 inches in diameter. By this means the 

 contents of the inner vessel can be kept constantly at a temperature 

 of 40° C. The lower end of the inner vessel is connected with a tube 

 which passes through the side of the outer vessel, so that its contents 

 may be drawn off and renewed whenever it may be desired to do so. 

 The material to be digested is placed in a U _sna P e d loop of parch- 

 ment-paper tubing, together with the digestive fluid, and this loop 

 is then allowed to hang down freely into the inner vessel, and is 

 surrounded by a fluid whose composition is the same as that of the 



