De Zouche. — Bacteria and their Relation to Disease. 33 



cesses of disease, as well as those of health, to ordinary 

 chemical laws. To these were opposed the vitalists, repre- 

 sented by Van Helmont (born 1577 or 1578), who attributed 

 disease to the disturbances of the vital spirits. These were 

 termed archeus, or, as there were two chief vital principles, 

 archei. They reigned in the stomach and spleen, and domi- 

 nated the body therefrom, delegating their powers to satraps 

 or minor archei, for the other organs. The belief in a "vital 

 principle" has prevailed since the beginning of medicine, or 

 of biology as a science. The arteries were supposed to con- 

 tain air, the origin of life, and to convey with it, or in it, the 

 vital spirits throughout the body. Hippocrates, as already 

 mentioned, held the theory of a vital principle, which he 

 believed was in the air, and was drawn in by the breath. 

 Even in the seventeenth century there was not much advance 

 on the Hippocratic pathology. The great English physician, 

 Sydenham (born 1634), attributed the origin of acute diseases 

 to a latent and inexplicable alteration of the air infecting the 

 bodies of men. He speaks of peccant matter, its concoction, 

 fermentation, and despumation. 



The humoral theory was opposed by that of the solidists, 

 who referred all diseases to an affection of the solid parts of 

 the body. They held that the solids alone were endowed with 

 vital properties, and alone could receive the impression of 

 agents tending to produce disease. 



So far for the general theories which influenced medical 

 thought and practice for centuries. They were destined to be 

 undermined or modified by the more accurate study of human 

 anatomy, which had received such an impetus from the labours 

 of Vesalius (born 1514), in the middle of the sixteenth century, 

 the discovery of the circulation of the blood by Harvey (1616), 

 and especially by the use of the microscope, wdiich Leeuwen- 

 hoeck improved materially, and employed in physiological and 

 biological investigation, with important results, towards the 

 end of the seventeenth century. 



Pathology, which may be called the physiology of disease, 

 began to emerge from the cloudland of theory into a clearer 

 day, but there were still many things obscure, and which 

 required better methods than were then at command for their 

 elucidation. The phenomena of inflammation especially occu- 

 pied the attention of pathologists, who believed that in these 

 lay the key to many or most of the morbid changes in 

 the body. Inflaumiation, from being regarded as a disease, 

 came to be understood as a condition of an organ or part 

 induced by some irritation — a process sometimes conservative, 

 sometimes destructive. And recent researches have show^n the 

 importance of a correct understanding of this process, for in 

 studving inflamed tissues with the aid of the microscope the 

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