216 ON THOUGHT IN MEDICINE. 



the first half of the last century, was professor of 

 chemistry and pathology in Halle. Stahl had a clear 

 and acute mind, which is informing and stimulating, 

 from the way in which he states the proper question, 

 even in those cases in which he decides against our pre- 

 sent views. He it is who established the first compre- 

 hensive system of chemistry, that of phlogiston. If we 

 translate his phlogiston into latent heat, the theoretical 

 bases of his system passed essentially into the system 

 of Lavoisier ; Stahl did not then know oxygen, which 

 occasioned some false hypotheses ; for instance, on the 

 negative gravity of phlogiston. Stahl's * soul of life ' 

 is, on the whole, constructed on the pattern on which 

 the pietistic communities of that period represented to 

 themselves the sinful human soul; it is subject to 

 errors and passions, to sloth, fear, impatience, sorrow^ 

 indiscretion, despair. The physician must first appease 

 it, or then incite it, or punish it, and compel it to 

 repent. And the way in which, at the same time, he 

 established the necessity of the physical and vital 

 actions was well thought out. The soul of life governs 

 the body, and only acts by means of the physico- 

 chemical forces of the substances assimilated. But it 

 .has the power to bind and to loose these forces, to allow 

 them full play or to restrain them. After death the 

 restrained forces become free, and evoke putrefaction 

 and decomposition. For the refutation of this hypo- 



