This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
In annulosa the nervous system consists of ganglia in each segment united together by nervous bundles. These bundles in general appearance correspond with the gangliated cord of the sympathetic in higher animals. The spinal cord is absent: we might therefore expect that drugs which act specially on the spinal cord in vertebrates would not have the same marked action on annelida, and this appears to be the case. It was found by Moseley that strychnine had no action on cockroaches;1 and leeches, when placed in water containing strychnine, become elongated but do not exhibit signs of tetanus. Some years ago I noticed that ants sprinkled with insect-powder died in violent convulsions, and it occurred to me that possibly substances which excite movements of the intestine in the higher animals might have a somewhat convulsant action on invertebrates. I therefore tried the effect of oil of peppermint on leeches, and it produced in them violent excitement. This appears to be of a somewhat convulsant nature : the animal at first flying rapidly hither and thither through the water, and afterwards, when it becomes quiet and nearly exhausted, there is a constant rhythmical twitching movement in the body which appears to last nearly until death. But if my idea had been correct, all carminatives should excite convulsions in annulosa. This is not the case, for the oils of peppermint, caraway, and anise have no apparent effect on black-beetles other than that of making them sluggish.
1 M. Foster, Pfliiger's Archiv, v. 191.
2 Dew-Smith, Proc. Roy. Soc.t March 18, 1875, p. 336.
Chloroform, ether, and other substances belonging to the alcohol group, act as anaesthetics on mammals, temporarily abolishing the functional activity of the brain, spinal cord, and medulla. On annulosa they have a similar action, although Krukenberg2 supposed they had a different effect, coagulating the muscular substance and rendering it stiff and hard before affecting the nerves. The experiment by which he thought this was proved consisted in applying chloroform to the middle part of a leech while the two ends of the animal were protected from the action of the vapour. The middle part then became stiff and rigid, but the movements of the two ends of the animal were perfectly co-ordinated, so that its actions were that of a single animal having a stiff girdle surrounding its middle. Ether and alcohol had a similar result. The co-ordination of the two ends showed that although the muscles had been rendered rigid by chloroform, the nerves which passed through the middle part of the body were still functionally active. When the middle part of the body was coagulated by the application of hot water, the muscles became rigid but the nerves were also destroyed, and the movements of the two ends of the animal were no longer co-ordinated, so that they appeared like two distinct animals connected by a rigid cylinder. Luchsinger3 repeated Krukenberg's experiments, and found that although the muscles were affected by the chloroform, yet the nervous system was still more sensitive than the muscles.
Fig. 33. - Krukenberg's apparatus for investigating the action of chloroform, etc, on annulosa. a is a shallow vessel containing a little water. 6 is a beaker containing water, saturated with chloroform, or ether, and covered with a piece of millboard c, in which are two holes. Through these holes the head and tail of a leech, d, are drawn and fastened by ligatures held by two-clamps. e is a bell-jar covering the whole.
1 Moseley, unpublished experiment made in C. Ludwig's laboratory.
2 Krukenberg, Vergleichend. physiologische Studien, Abtg. I., p. 77.
3 Luchsinger and Guillebeau, Pfliiger's Archiv, xxviii., p. 61.
Atropine has a similar action to chloroform, ether, and alcohol, on the muscles of the leech. Veratrine appears to some extent to affect the muscles, so that after contraction they relax slowly. It appears also, however, to affect the nerve-centres, and, according to Krukenberg, paralyses more especially the sensory centres. Camphor, strychnine, morphine, caffeine, copper sulphate, and mercuric chloride act chiefly on the nervous system of leeches, although they also affect the muscles when applied for a length of time. Caffeine renders the muscles in the leech also rigid.