CHAP. XVI] ANyESTHETIGS— HUMANE DESTRUCTION 



189 



limbs, which we will consider from the point 

 of view of local anaesthesia later in the chapter. 

 In the thorax there are seventeen double pairs 

 of dorsal nerves, the first and second forming 

 part of the brachial plexus. Farther back, 

 towards the tail, there are in the abdomen six 

 double pairs of lumber nerves, the fourth, fifth 

 and sixth helping to form the lumbar-sacral 

 plexus, which sends off the nerves to the hind 

 limbs. Farther back there are five double pairs 

 of sacral nerves, situated in the pelvic cavity, 

 the first, second and third helping to form the 

 lumbar-sacral plexus. Lastly, there are six or 

 seven double pairs of coccygeal nerves that 

 supply the muscles of the tail. 



732. P. 137 and 138a show the nerves given 

 off by the brachial plexus and lumbar-sacral 

 plexus, and the places where the cocaine, etc., 

 would be injected as a local anaesthetic. 



As well as the large number of motor nerves 

 which branch into the hundreds of smaller 

 nerves, all of which have their own names and 

 special functions (for instance, the fifth cranial 

 nerve branches into nineteen main nerves, each of 

 which subdivides and re-subdivides many scores 

 of times), there is the sympathetic system, that 

 assists in controlling the involuntary functions of 

 the body, and is in immediate contact with the 

 motor system, briefly described above. 



The sympathetic system consists of a double 

 chain of ganglion bodies extending from the 

 head to the tail, outside and below the vertebral 

 column. There are five main groups in the sym- 

 pathetic system : the cephalic ganglia, in the 

 head ; the cervical ganglia, in the neck ; the 

 dorsal, or thoracic, ganglia, in the thorax or 

 chest, which forms the great splanchnic gang- 

 lion, solar ganglion and the solar plexus, that 

 gives ofi nerve branches to most of the abdominal 

 viscera ; the lumbar, or abdominal, ganglia ; 

 and, lastly, the sacral, or pelvic, ganglia. 



This chain of ganglia ends just below the 

 first coccygeal vertebra. 



The reader will gather from the above some 

 idea of the extraordinarily complex nervous 

 mechanism the horse or human being possesses. 

 In the horse the motor nerves in the spinal cord 

 are better developed, whilst in the human being 

 the brain is better developed. It is easy to realise 

 how soon the nervous system can be upset and 

 how difficult it often is to repair nervous dis- 

 orders or breakdowns. 



733. Brief Description of the Nervovs Tissue. 

 — The nerve tissue is divided into a central 

 nervous system (brain and spinal cord), smaller 

 centres or ganglia, nerves, and nerve endings 

 (special senses). In the embryo the nervous 

 system is formed from the epiblast (or ectoderm). 

 Each individual nerve consists of a dendrite, 

 that carries an impulse to the cell body of the 

 nerve, the cell body (or ganglion cell), and the 

 neuraxis, that carries the impulse from the cell 



body to a muscle, blood-vessel, gland, etc. The 

 whole is called a neurone. 



Those that cause muscular contraction are 

 called motor, and those that convey sensation are 

 called sensory. The cell body contains, amongst 

 other things, minute chromatophile granules, 

 which, under such conditions as diseases of the 

 nervous system, poisoning, and excessive fatigue, 

 disappear altogether. 



734. Thus a nerve fibre may consist of a 

 number of neuraxes, or dendrites, or both. The 

 cell bodies are situated in the brain, spinal cord, 

 or the sympathetic ganglia (e.g., solar plexus, 

 situated posteriorly to the liver in the horse). 



The nerve fibres are made up of little fibrils 

 and neuroplasm, which is the matrix, sur- 

 rounded by a skin (axolemma). It is often 

 surrounded again by a medullary sheath and an 

 outer sheath of Schwann (or neurilemma), and 

 outside this is Henle's sheath, which is always 

 present. The medullary sheath is absent at 

 certain intervals along the nerves, leaving a dip 

 in the surface, called the node of Randier ; it is 

 at these nodes that nerve branches originate. A 

 nerve trunk (which we see if we dissect an 

 animal, and which rather resembles white cord) 

 consists of several bundles of nerve fibres, each 

 bundle being called a funiculus. Each funiculus 

 consists of a number of nerve fibres in their 

 respective sheaths. The end of the nerve varies ; 

 some end like a brush, others in a node. 



Brief History of Anaesthetics 



735. The ancient writers were aware that 

 certain herbs had the effect of producing in- 

 sensibility to pain. Pliny, Galen, Dioscorides 

 and Isodorus all mentioned that certain roots 

 and herbs had the power of paralysing sensation 

 and motion. 



In the reign of Henry VIII. a doctor used a 

 herb, probably mandragora, to cause insensi- 

 bility to pain. It was also known that the 

 vapours of certain drugs, as well as the use of 

 drugs administered orally, had this effect. The 

 discovery of oxygen by Joseph Priestley (1774) 

 caused the importance of the inhalation of gases 

 to be brought to light. 



Sir Humphry Davy, in 1799, first discovered 

 the anaesthetic properties of laughing gas 

 (nitrous oxide, N^O). 



Faraday, in 1818, also made some experiments 

 with sulphuric ether. Progress was very slow. 

 In 1831, Samuel Guthrie, an American — and in 

 the same year, Soubeiran and Sir James Young 

 Simpson (Edinburgh) — independently procured 

 by distillation a substance from chloride of lime 

 and alcohol. This preparation was submitted to 

 Dumas, who called it chloroform (CHCl,), on 

 account of its similarity in composition to formic 

 acid. 



Jacob Bell and M. Flourens also experimented 



