1 98 DIGESTION. [CHAP. xxiv. 



stomach. He obtained some of this fluid by making animals swal- 

 low sponges, which he could draw out of their stomachs by a string 

 attached : and thus he was enabled to institute experiments on arti- 

 ficial digestion, so as to shew that alimentary substances out of the 

 body could be altered by this fluid in the same manner as they are 

 changed in the stomach. He likewise introduced food into the 

 stomachs of animals in perforated tubes, whereby they were defended 

 from the pressure of the walls of the stomach, but could imbibe its 

 fluids. His experiments disproved the favourite theory of the day, 

 which ascribed all changes of the food in stomach digestion to the 

 influence of trituration upon it by the action of the muscular coat 

 of the stomach : they shewed that the trituration in the gizzard of 

 birds was no more than mastication by teeth in other animals, and 

 that digestion was accomplished in birds of prey, dogs, &c., and 

 probably in man, by the action of a fluid which exerted a solvent 

 influence upon the food.* 



Spallanzani likewise illustrated this subject by numerous experi- 

 ments upon vertebrate animals of all classes, and even upon himself. 

 Following the plan of Reaumur, he obtained the gastric juice by 

 means of sponges, and he introduced food into the stomachs of 

 animals enclosed in perforated tubes and balls. His essay on the 

 subject of digestion is one of the most interesting dissertations 

 in the literature of physiology, and is full of facts proving the 

 secretion of a fluid capable of reducing and dissolving alimentary 

 substances. 



Stevens availed himself of a rare opportunity of investigating 

 the effects produced on food in the human stomach. A hussar had 

 accustomed himself at the early age of seven to swallow stones and 

 other hard bodies; and, having continued the practice during twenty 

 years, what had originated in idle amusement was now resorted to 

 as a regular profession, to supply the necessaries of life. When Dr. 

 Stevens first saw him, his stomach was so distended, apparently by 

 the considerable weight to which it was repeatedly exposed, that 

 he could swallow several stones at once, which were not only felt in 

 the stomach, but might be heard by the bystanders moving against 

 each other when the hypogastric region was struck. 



Dr. Stevens made this man swallow perforated silver balls, con- 

 taining sometimes raw animal food, sometimes vegetable substances : 

 in general, raw animal substances suffered less than those which 

 were roasted or boiled ; roasted or boiled animal substances which 



* Mem. de 1'Acad. des Sciences, an. 1752, pp. 705 752. 



