SEVENTEENTH AND EIGHTEENTH CENTURIES 1 77 

 Hoffmann's practical ivork and bis theory 

 Undoubtedly Hoffmann's services to science lie principally in the sphere of 

 practical medicine. He described several diseases hitherto unaccounted for; 

 both in theory and in practice he insisted upon accurate diagnosis based upon 

 natural-scientific principles, considerate treatment of the sick, and simple 

 medicines. He himself made up and sold at a great profit quite a number of 

 preparations, which still play their part in popular medicine. He was a very 

 productive writer on medical subjects in every conceivable specialized sphere, 

 but he also tried to combine in one general theory of the functions of the body 

 the principles at which he had arrived in the course of his work, and this 

 theory has not been without its importance for the general development of 

 biology. It takes as its starting-point the so-called chemiatric theories preva- 

 lent in the seventeenth century, which ultimately originated in Paracelsus's 

 fantastic speculations as to the human body's being composed of quicksilver, 

 sulphur, and salt, and in conformity with its original sought to explain the 

 functions of the body as essentially phenomena of chemical change, for which 

 purpose recourse was had either to the mechanical theories of the movements 

 of the body, described in the foregoing, or else to the mass of mystical specu- 

 lations still available at that time, to fill up the gaps in the proposed system. 

 Hoffmann takes his stand at the very start on chemico-mechanical ground. He 

 himself was a clever chemist and besides possessed a complete mastery of the 

 anatomical literature of his age, in which sphere both Borelli and Perrault 

 had some influence on him; and, finally, he had not neglected the discoveries 

 of either Newton or Leibniz. He began with the principle that matter and 

 motion form the foundation of existence; the body is a machine, which is 

 kept going by the circulation of the blood. Life is thus a purely mechanical 

 process, from whose functions the activities of the soul can be excluded; 

 when the body dies, it is not the soul that leaves the body, but the body that 

 abandons the soul, so that the latter can no longer use the organs of the body 

 as its tools. The movement of the blood is caused by the heart; the latter's 

 action, again, is regulated by the movements in the nervous system, in the 

 fibres of which there circulates a fluid, "sfiritus animalis," which is formed 

 of extremely light ether-particles and is produced in the brain and by its 

 movements induces and regulates the muscular functions, sense-impressions, 

 and alimental processes. The power of the blood to maintain life is due to 

 the fact that it contains a "spiritus" formed of the ether constituents of the 

 air and the sulphurous element in the blood. Chemically, in fact, the com- 

 ponents of the blood are partly sulphurous, partly ethereal, and partly 

 earthy; the sulphur element is the cause of the warmth of the body, both the 

 natural warmth and that increased by inflammation, which is induced by 

 the sulphur particles easily becoming extremely mobile through the action 

 of the ether. The function of the lungs is to mingle the component parts of 



