ANATOMY AND PHYSIOLOGY 



cular movements: elasticity, or "dead nervous force"; 

 irritability, or " innate nervous force"; and nervous 

 force in itself. And in 1752 he described one hundred 

 and ninety experiments for determining what parts of 

 the body possess "irritability" that is, the property 

 of contracting when stimulated. His conclusion that 

 this irritability exists in muscular substance alone and 

 is quite independent of the nerves proceeding to it 

 aroused a controversy that was never definitely settled 

 until late in the nineteenth century, when Haller's 

 theory was found to be entirely correct. 



It was in pursuit of experiments to establish his 

 theory of irritability that Haller made his chief dis- 

 coveries in embryology and development. He proved 

 that in the process of incubation of the egg the first 

 trace of the heart of the chick shows itself in the thirty- 

 eighth hour, and that the first trace of red blood showed 

 in the forty-first hour. By his investigations upon the 

 lower animals he attempted to confirm the theory that 

 since the creation of genus every individual is derived 

 from a preceding individual the existing theory of 

 preformation, in which he believed, and which taught 

 that "every individual is fully and completely pre- 

 formed in the germ, simply growing from microscopic 

 to visible proportions, without developing any new 

 parts." 



In physiology, besides his studies of the nervous 

 system, Haller studied the mechanism of respiration, 

 refuting the teachings of Hamberger (1697-1755), who 

 maintained that the lungs contract independently. 

 Haller, however, in common with his contemporaries, 

 failed utterly to understand the true function of the 



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