Histology

Another technique that was flourishing and available to scientists studying the autonomic system was histology. The compound microscope had been invented by Robert Hooke in 1665, but the lenses suffered from chromatic aberration, and it was only after the development of achromatic lenses and achromatic compound microscopes (the first good one constructed in 1826 by J.J. Lister, father of the antisepsis Lister) that the structure of cells could be made out, and neurones visualised. Although Purkinje in 1837 described the large neurones in the cerebellum that bear his name, and in spite of some other minor advances, improvements in fixing and staining techniques were required before the details of the neuronal structure and the links between neurones and the nerve fibres could be elucidated. The credit for the most marked advances in the histological study of nervous tissue goes to Camillo Golgi, the Italian who perfected a silver staining technique in 1872 that allowed fine details of individual neurones to be studied, and Santiago Ramon y Cajal, a young Spaniard, unknown to the scientific community before 1889, whose beautiful and detailed histological works using Golgi's techniques led to them sharing the Nobel prize for medicine in 1906. The early works on neurones and the links between them had split the scientists into two camps: those following the reticular theory, who believed that the nerves formed an interconnecting network, and those following the neurone theory, who believed that the neurones were individual elements.

Even in 1906, the controversy was still apparent; in their speeches at the chapter i

Nobel prize ceremony it was clear that Golgi followed the reticular theory Historical and Ramon y Cajal followed the neurone theory. Background

It is interesting to note that the autonomic physiologists, such as Langley, were at that time mapping the positions of the ganglia in the autonomic nervous system not by histological studies, but by pharmacological ones - they had discovered that when nicotine was applied (with a paintbrush), it would first activate and then inactivate the neuronal pathway under study, but only if applied to the ganglia. Thus activation by nicotine implied the presence of neurones in the pathway. Incidentally the fact that nicotine then blocked transmission through the pathway was possible evidence against the reticular theory, and the autonomic physiologists were already speculating that chemical transmission occurred between neurones.

1.2.3 General anaesthesia

Analysis of the functional aspects of the system depended largely on the advent of general anaesthesia, which only began to be used with tooth extraction under ether by Henry Morton in 1846, and for the relief of the pain of childbirth by lames Simpson with chloroform in 1847. General anaesthetics, combined with the skilled surgical and observational techniques and the curiosity of the anatomists and physiologists in the second half of the 19th century, greatly furthered understanding of the autonomic nervous system.

In anaesthetised animals, the parts of the body that were obviously working were of course the involuntary systems, and it was comparatively easy for physiologists to record such things as heart rate, blood pressure, gastrointestinal motility, pupil diameter, piloerection, and the production of various secretions.

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