DOCTRINE OF ACID AND ALKALI. 263 



counteracting and neutralizing the activity of the other. The notion 

 of such opposition and neutrality is applicable to a very wide range of 

 chemical processes. The person who appears first to have steadilv 

 seized and generally applied this notion is Francis de la Boe Sylvius ; 

 who was born in 1614, and practised medicine at Amsterdam, with a 

 success and reputation which gave great currency to his opinions on 

 that art. 1 His chemical theories were propounded as subordinate to 

 his medical doctrines ; and from being thus presented under a most 

 important practical aspect, excited far more attention than mere theo- 

 retical opinions on the composition of bodies could have done. Sylvius 

 is spoken of by historians of science, as the founder of the iatro-che- 

 mical sect among physicians ; that is, the sect which considers the dis- 

 orders in the human frame as the effects of chemical relations of the 

 fluids, and applies to them modes of cure founded upon this doctrine. 

 We have here to speak, not of his physiological, but of his chemical 

 views. 



The distinction of acid and alkaline bodies (acidum, lixivutn) was 

 familiar before the time of Sylvius ; but he framed a system, by con- 

 sidering them both as eminently acrid and yet opposite, and by apply- 

 ing this notion to the human frame. Thus 2 the lymph contains an 

 acid, the bile an alkaline salt. These two opposite acrid substances, 

 when they are brought together, neutralise each other (infringunt), 

 and are changed into an intermediate and milder substance. 



The progress of this doctrine, as a physiological one, is an important 

 part of the history of medical science in the seventeenth century ; but 

 with that we are not here concerned. But as a chemical doctrine, this 

 notion of the opposition of acid and alkali, and of its very general 

 applicability, struck deep root, and has not been eradicated up to our 

 own time. Boyle, indeed, whose disposition led him to suspect all 

 generalities, expressed doubts with regard to this view ; s and argued 

 that the supposition of acid and alkaline parts in all bodies was pre- 

 carious, their offices arbitrary, and the notion of them unsettled. 

 Indeed it was not difficult to show, that there was no one certain crite- 

 rion to which all supposed acids conformed. Yet the general concep- 

 tion of such a combination as that of acid and alkali was supposed tc 



1 SprengeL Geschichte der Arzneykunde, vol. iv. Thomson's History of 

 Chemistry in the corresponding part is translated from Sprengel. 



2 De Methodo Medendi, Amst. 1679. Lib. ii. cap. 28, sects. 8. and 53. 



3 Shaw's Boyle, iii. p. 432. 



