METHODS OF PHYSIOLOGICAL RESEARCH 19 



nomena, and they distinguished several varieties. The " nisus 

 formativus," e.g., or peculiar " formative effort," offered a simple 

 explanation of the forms of organisms, accounting for the facts that 

 from the egg of a fowl a fowl and no other species always developed, 

 and that the offspring of dogs are always dogs. In place of a real 

 explanation a simple phrase, such as " formative effort," or " vital 

 force," was satisfactory, and signified a mystical force belonging to 

 organisms only. Thus it was easy to " explain " the most complex 

 vital phenomena. 



But some investigators were not content with this kind of 

 explanation, and, while indifferent to the doctrine of vital force, 

 continued to search for a cheniico-physical explanation of vital 

 phenomena. They received a strong stimulus from the new 

 discoveries of Galvani (1737-1798), who proved that electricity is 

 produced by the living animal body, especially by the nerves. 

 Naturally the value of this fact was very soon overestimated, and 

 under the ban of the prevalent philosophy of nature, particularly 

 as a result of the researches of Ritter (1776-1810) and partly also 

 those of Alexander von Humboldt (l769-1859) and others, who 

 extended Galvani's experiments, the idea arose and later became 

 very popular, that the galvanic current is the cause of all vital 

 phenomena, and even that all phenomena of all nature may be 

 explained in general by galvanic polarity. 



The great cheviical discoveries of the previous century also 

 influenced the development of physiology. Vegetable physiology 

 was especially advanced by Ingenhouss (1730-1799), who developed 

 the theory of the consumption of carbonic acid by plants. The 

 discovery of oxygen by Priestley (1733-1804) and Lavoisier (1743- 

 1794), which was so momentous for physiology, bore its first fruits 

 when Girtanner (1760-1800) showed that venous blood receives 

 oxygen in the lungs from the inspired air. Thus the old doctrine 

 of the pneuma, which controlled physiological ideas for centuries, 

 was justified in modern form, and at the same time the ingenious 

 idea of Mayow, who had compared respiration to a process of com- 

 bustion, was raised to the rank of a fundamental physiological 

 fact. 



Besides the physical and chemical discoveries of that time, those 

 in anatomy led also to important physiological results. Most 

 prominent among these was the fundamental law of special nerve- 

 physiology, announced by Charles Bell (1774-1842), and later 

 proved experimentally by Johannes Mliller, which affirms that 

 the posterior roots of the spinal nerves are sensory (conducting 

 centripetally), while the anterior roots are motor (conducting 

 centrifu gaily). 



Finally, in microscopy Spallanzani (1729-1799), and later 

 especially Treviranus, obtained the distinction of having dis- 

 proved experimentally by careful researches the theory of the 



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