SEVENTEENTH AND EIGHTEENTH CENTURIES 185 

 days, a thorough knowledge of the entire range of the then known medical 

 and biological literature. The common biological, or, as he termed it, phys- 

 iological, section of his principal work, Institutiones medicce, gives the im- 

 pression, owing to the mass of second-hand information that he imparts 

 when quoting his sources, of being to a certain extent a compilation — in 

 fact, it was published with the expressed intention of providing a handbook 

 for instructional purposes — but the ideas he presents in it are at any rate 

 thought out on entirely original lines, and the whole work seems, in com- 

 parison with Hoffmann's or Stahl's theoretical speculations, strikingly 

 modern. The abstract theories are, as a matter of fact, entirely thrust into 

 the background in favour of a close analysis of all the known facts relating 

 to the functions of the body. First he describes the digestion, starting with a 

 detailed account of mastication; then the functions of the digestive canal 

 and its glands; then the circulation of the blood, and respiration, the brain 

 and nervous system, several glandular systems, the muscles, the skin, sen- 

 sations, and reproduction. From a purely anatomical point of view the 

 presentation does not on the whole differ from the results achieved in modern 

 times; we find here that he has taken full advantage of every step of progress 

 made by such people as Borelli, Malpighi, and Ruysch. In particular 

 Ruysch's careful dissections and injections Boerhaave, who, indeed, was a 

 personal friend of his, was able to take advantage of in a masterly way. 



Hij" mechanical conception of life 

 When he comes to explain the functions of the different organs, he bases his 

 ideas on a strictly mechanical conception: the action of the body is motion; 

 "the power to exert movement is called function, which takes place in ac- 

 cordance with mechanical laws and only by them can be explained." Thus 

 both the disintegration and assimilation of food in the body are purely 

 mechanical — ■ he denies that the gastric juices have any chemical reaction — 

 the principal agent is the body's own heat and the constant movements of 

 the digestive canal and its surrounding organs, but the nervous fluid also 

 plays a predominant part in the functions of the body. With regard to the 

 question of the "cooking" of food in the digestive canal, as assumed by 

 ancient authors, Boerhaave takes up a somewhat sceptical attitude. On the 

 other hand, he believes that acrid and unsuitable food-substances become ex- 

 cluded by contracting the openings of the chyle vessels into the bowel. Such 

 food as has been taken into the chyle vessels is conveyed through the thorax 

 to the venous system; there blood and chyle are mingled, and this mixture 

 becomes complete through the blood's passing into the lungs, whose porous 

 structure serves to render the mixture as thorough as possible. In a conten- 

 tious article written against Borelli, who believed it to be the case, he denies 

 that the air from the lungs passes into the blood; Boerhaave is unable to 

 explain why it is that living creatures cannot breathe in an unventilated 



