156 Sylvius and his Pupils. [lect. 



called chylification. The second stage, according to him, is 

 due to interaction of the bile and pancreatic juice. We have 

 seen that De Graaf tried to persuade himself, by taste chiefly, 

 that the pancreatic juice was acid, and indeed the acidity of the 

 pancreatic juice was a foundation-stone of Sylvius's views on 

 digestion. Although, as we have seen, his chemical inquiries 

 were chiefly concerned with acids, alkalis and bases, and he was 

 above all other men of his time qualified to speak about such 

 things,, although he might have been expected to be one of the 

 first to recognize that pancreatic juice was alkaline, he never- 

 theless, led away apparently by preconceived theory, always 

 insisted that it was acid. Its use in digestion was, he said, and 

 De Graaf repeated it, to effervesce, to ferment, with the bile. 

 Sylvius says, 



" It is impossible that the juice of the pancreas in some 

 " degree or mode so acid should be mixed with the bile, 

 " abounding as this does in bitter and volatile salt, without 

 " exciting an effervescence, as may be proved by endless ex- 

 amples seen in chemistry and elsewhere." 



So also De Graaf : " That effervescence is excited by the 

 " mixture of pancreatic juice which abounds in acidity, with bile 

 " which abounds in volatile and fixed salt, we dare all the more 

 " boldly assert, since hitherto we have met with no example 

 " of an acid spirit meeting with a lixivious salt {i.e. a soluble salt 

 "derived by washing ashes) without a manifest effervescence 

 " resulting, provided impediments are removed." 



De Graaf recognized the difficulty presented by the fact that 

 when bile and pancreatic juice are mixed together out of the 

 body they do not effervesce ; but he overcomes this by arguing 

 that in this as in so many other cases a suitable temperature 

 is needed. " However it be, no one ought to wonder that we 

 " cannot demonstrate an effervescence between bile and pan- 

 " creatic juice when these are mixed together outside the living 

 " body, since neither artificial heat nor the natural warmth of 

 " the hand can excite such a heat as we know exists in the 

 " small intestine . on account of the surroundings of the very 

 " warm viscera." 



He also notices the objection that the dilution of the mixed 



