0»38 GEORaE E. NICHOLLS. 



longer be maintained, and the question of its function (and that of the 

 related sub-eommissural organ) is reopened. 



The supposed inaccessibility of the fibre had led Sargent to operate 

 upon it in the region of the hind-brain, and his experiments were 

 therefore open to the serious objection that they involved great risk of 

 grave damage to the brain itself. My discovery, however, that the 

 fibre is, in the lower vertebrates at any rate, comparatively readily 

 accessible in the region of the tail (where it actually passes out of the 

 central canal of the sheltering spinal cord through the terminal pore), 

 suggested the practicability of experimental work upon Eeissner's 

 fibre without danger of damage to the central nervous system. 



The experiments, which consisted simply in breaking the fibre by a 

 slight incision at the end of the filum terminale, were carried out in the 

 Laboratory of the Marine Biological Station at Plymouth, in the 

 summers of 1910 and 1911, and I desire here to acknowledge my 

 obligations to the British Association for the Advancement of Science, 

 and the Senate of London University for the use of their Tables, and also 

 to the Eoyal Society for a Grant which enabled me to carry out the more 

 extensive series of experiments in 1911. My thanks are also due to 

 Dr. Allen and tiie other members of the staff for the courteous way in 

 which they met my wishes and facilitated the carrying out of the work. 



In all, the experiment was carried out upon some seventy specimens 

 (dogfish and rays), and a short account of the earlier experiments has 

 already been published (Anat. Aiiz., Bd. XL, pp. 409-432). In compli- 

 ance with the conditions under which the licence to conduct the 

 experiments was granted the specimens were anajsthetized — a most 

 unnecessary precaution (in view of the trivial character of the opera- 

 tion, which rarely drew a drop of blood), and one which, in the case of 

 some of the subjects of experiment, proved a much more serious 

 matter than the operation itself. 



L'l'pon these amvsthetized specimens the necessary prick was quickly 

 inflicted and the specimens returned to the tank. Subsequent observa- 

 tion (extending in different cases over a period of less than an hour 

 to as much as three weeks or more) showed that apart from a slightly 

 different action in swimming, which I found almost impossible to 

 analyse and describe, the only discoverable eflect of the operation was 

 that many of the specimens when at rest adopted a pose which was 

 markedly unlike that of the normal animal. In the normal specimen 

 at rest the under surface of the head and the lower lobe of the caudal 

 fin touch lightly upon the supporting surface, and the entire long axis 

 of the body extends in a straight line. In these subjects of the 

 experiments (in which subsequent microscopic examination of the 



