150 Sylvius and his Pupils. [lect. 



Sylvius as I have said followed van Helm on t in considering 

 a large number of the changes taking place in the living body 

 as being of the nature of fermentative processes ; but his idea 

 of fermentation was a different one from that of van Helmont. 

 The latter taking vinous fermentation as the type saw in the 

 ferment which produced the change a subtle agency, having 

 characters of its own, one whose effects were wholly different 

 in kind from ordinary chemical events, from the result for 

 instance of adding a base, such as lead oxide, to an acid, 

 such as vinegar. The action of the ferment was in van 

 Helmont's eyes of a more exquisite nature than a simple 

 chemical change ; the bubbles of gas which appeared in the 

 fermenting vat were incidental things, not features essential 

 to the action of the ferment. Sylvius saw nothing of all these 

 subtle distinctions. To him the rising of the bubbles of gas, 

 without the intervention of an extrinsic blast of air, seemed to 

 be one of the essential facts of fermentation ; and since he saw 

 the same spontaneous escape of gas when an acid was poured 

 over an earth or a salt, when oil of vitriol for instance was 

 poured over chalk, he concluded that the two processes were 

 identical in kind. Hence, though he continued often to use 

 the word ' fermentation,' he more often used the word ' effer- 

 vescence,' and at times seems to use the one or the other quite 

 indifferently. 



Vieussens, who in addition to the researches in anatomy 

 which have handed down to us the terms ' valve of Vieussens ' 

 and 'annulus of Vieussens,' busied himself with chemical 

 matters, writing in 1688, Be natura etc. Fermentationis, thus 

 formally defines the various kinds of fermentation : 



" Fermentation is the adventitious and expansive movement 

 "of heterogeneous parts and of insensible fermenting bodies 

 " excited without sensible cause, which, when it is vehement 

 '■ or of long duration, brings about an essential change or a 

 " conspicuous alteration in the fermenting bodies themselves. 



" Latent fermentation, than which nothing is more common 

 * alike in the works of nature and of man, is an adventitious 

 " and expansive movement of heterogeneous parts and insensible 

 "bodies excited without sensible cause, which, when it is 



