222 The Physiology of Digestion [lect. 



M to earth ; therefore must be widely different from digestion 

 " which converts both animal and vegetable substances into 

 " chyle, in the formation of which there cannot be a de- 

 " composition similar to fermentation. 



"Digestion is likewise very different from chemical solution, 

 " which is only a union of bodies by elective attraction. But 

 " digestion is an assimilating process ; and in this respect is 

 "somewhat similar in its action to that excited by morbid 

 " poisons. It is a species of generation, two substances making 

 " a third ; but the curious circumstance is its converting both 

 " vegetable and animal matter into the same kind of substance 

 " or compound, which no chemical process can effect. The chyle 

 "is compounded of the gastric juice and digestible substances 

 "when perfectly converted; and it is probable that the quantity 

 " of gastric juice may be nearly equal to that part of the food 

 "which is really changed into chyle." 



Hunter's views here it will be seen are very similar to those 

 of Spallanzani, though modified by the vitalistic Stahlian 

 conceptions in which the latter did not share. In one respect 

 Hunter went beyond Spallanzani ; he was, at least at one time, 

 inclined to attach importance to the acidity of gastric juice. 

 In 1772 he says: "In all the animals, whether carnivorous or 

 " not, upon which I made experiments to discover whether or 

 " not there was an acid in the stomach (and I tried this in a 

 "great variety), I constantly found that there was an acid, 

 " though not a strong one, in the juices contained in that viscus 

 "in a natural state." But in his later paper he is led to think 

 that " it is only formed occasionally. Whether the stomach 

 " has the power of immediately secreting this acid, or first 

 " secretes a sugar which afterwards becomes acid, is not easily 

 " ascertained." He is inclined towards the latter view,, especially 

 since in the stomach of the calf before birth no acid can be 

 found. And indeed the eighteenth century passed wholly away 

 before the ' acid ferment ' on which van Helmont had, in the 

 early years of the seventeenth century, laid such great stress 

 was rightly appreciated. For the observation of Carminati, who 

 following close after Spallanzani, in 1785 found the clue to the 

 problem of the acidity of gastric juice, by shewing that in 



