MR. G-. J. ROMANES ON THE LOCOMOTOR SYSTEM OF MEDUSAE. 
743 
any poison on the central, peripheral, and muscular systems respectively *, he will not fail 
to appreciate the value of the foregoing observations. In reading over the whole list he 
will meet with an anomaly here and there ; but, on the whole, I do not think he cannot 
fail to be satisfied with the wonderfully close adherence which is shown by these ele- 
mentary nervous tissues to the rules of toxicology that are followed by nervous tissues 
in general. In one respect, indeed, there is a conspicuous and uniform deviation from 
these rules ; for we have seen that in the case of every poison mentioned more or less 
complete recovery takes place when the influence of the poison has been removed, even 
though this has acted to the extent of totally suspending irritability. In other words, 
there is no poison in the above list which has the property, when applied to the Medusse, 
of destroying life till long after it has destroyed all signs of irritability. What the 
cause of this uniform peculiarity may be is, of course, conjectural ; but I may suggest 
two considerations which seem to me in some measure to mitigate the anomaly. In the 
first place, we must remember that in the Medusae there are no nervous centres of such 
vital importance to the organism that any temporary suspension of their functions is 
followed by immediate death. Therefore, in these animals, the various central nerve- 
poisons are at liberty, so to speak, to exert their full influence on all the excitable tissues 
without having the course of their action interrupted by premature death of the 
organism, which in higher animals necessarily follows the early attack of the poison on 
a vital nerve-centre. Again, in the second place, we must remember that the method 
of administering the above-mentioned poisons to the Medusse was very different from 
that which we employ when administering them to other animals ; for, in the case of 
the Medusse, the nervo-muscular tissue is spread out in the form of an exceedingly 
tenuous sheet, so that when the animal is soaking in the poisoned water every portion 
of the excitable tissue is equally exposed to its influence ; and that the action of a 
poison is greatly modified by such a difference in the mode of its administration has 
recently been proved by Professor Gamgee, who found that when a frog’s muscle is 
allowed to soak in a solution of vanadium &c. it loses its irritability, while this is not 
the case if the poison is administered by means of the circulation. 
In conclusion, I may observe that in the case of all the poisons I have tried, the time 
required for recovery after the animal is restored to normal water varies immensely. 
The variations are chiefly determined by the length of time during which the animal 
has been exposed to the influence of the poison, but also, in a lesser degree, by the 
strength of the solution employed. To take, for instance, the case of caffein or chloro- 
form, if Sarsice are transferred to normal water after they first cease to move, a few 
seconds are enough to restore their spontaneity ; whereas if they are allowed to remain 
* The method of comparison consists, as will already have been gathered from the perusal of the foregoing 
sections, in : — first, stimulating the tentacles, and observing whether this is followed by such a discharge of the 
attached ganglion as causes the hell to contract ; next, stimulating the hell itself, to ascertain whether the 
muscular irritability is impaired ; and, lastly, stimulating either the tentacles or the hell, to observe whether 
the reciprocal connexions between tentacles, bell, and polypite arc uninjured. 
