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retain tlieir luminosity so long as they continue to possess 
organic contractility.* 
In short, it is to contraction, and to that alone, to which I 
consider the production of light attributable. This conclusion, 
however, was only arrived at after I had compared the results 
of two series of experiments — the one tried in the daytime, the 
other at night : these experiments being diversified, but each 
series in strict correspondence with the other. t Thus, I tested 
the action of heat, compression, electricity, and of ten chemical 
substances, alkaline, acid, and neutral, — the general result being 
that any agent whatsoever capable of causing the sarcodic sub- 
stance of the Noctilucie to contract, was efficacious in precisely 
the same degree and at the same time in producing phospho- 
rescence. An isolated shock caused, dining the daytime, a 
violent but momentary contraction ; at night it gave rise to a 
bright but transient exhibition of fight. Under the influence 
of continued, or of too violent irritation, the whole substance 
of the body is seen, in the daytime, to contract to such an extent 
as to become liberated from the external envelope, gradually to 
^ink down, as it were, and become disorganized or lose its vital 
properties. At night, the same operation leads to a continued 
phosphorescence apparently pervading the whole animal, and 
of which the steady and permanent brilliancy always denotes 
approaching dissolution. Thus, contraction and phosphores- 
cence are invariably met side by side, and proceeding, as it 
were, step by step.t 
The contraction may be either partial or general, and it may 
manifest itself in different places at the same time ; so also with 
the luminosity. This is easily observable with the aid of a 
pocket lens. It is only necessary to pour water containing 
Noctilucm into a tube and shake it a few times, when the 
little luminous spheres at once become clearly distinguish- 
able, and their movements may be readily followed. 
They will be found to present the appearance which I have 
sought to depict in fig. 2, A, B, and occasionally the same ani- 
malcule is seen to become illuminated at two points in succes- 
sion. If the tube be repeatedly shaken, or (what is a still more 
* I have ascertained the same thing to be the case in the locomotive 
organs of Annelides. 
t By this, I mean that I repeated at night the experiments tried during 
the daytime, in such a manner as to be able to compare the results. Thus, 
for example, whatever produced contraction during the daytime, imparted 
luminosity at night. 
t These experiments are not easy. The use of the compressor is requisite 
in their performance, and the operator must be an adept in its employment. 
It requires two persons to conduct the experiments by night. M. Bouchard 
was kind enough to co-operate with me in all these researches. 
