634 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



15th and l6th, it was still present; on the 17th, the lucidness began to diminish; 

 on the 18th, it was faint; and on the 19th it had vanished. — Exper. 11. June 

 11th, 6 other tadpoles were dropped into a solution of 1 dr. of common salt in 3 

 oz. of water. On the 12th and 13th, the menstruum was dark; on the 14th, it 

 had extracted from the tadpoles a very beautiful bright light; on the 15th, the 

 menstruum was exceedingly luminous; on the 16th and 17th, nearly the same: the 

 light then gradually faded, so that on the 21st it was merely visible; and on the 

 22d it disappeared. — Exper. 12. On the 21st of June, the above 2 experiments 

 were repeated; when the tadpoles remained in the menstruums till the 27th, but 

 no light was emitted. What was the cause of this failure in these 2 last experi- 

 ments ? Was it 10 days' increased growth of the animal, which was taken from 

 the same pond, that made the difference ? — Exper. 13. The above experiments 

 were repeated, when the tadpole had just put on the state of a frog, but without 

 producing any lucid appearance. 



The Light is incorporated with the whole Substance of Marine Fishes. 



Exper. 14. A fine fresh herring, being gutted, was divided longitudinally into 2 

 parts, both of which were hung up, by pieces of string, in the laboratory. On 

 the 2d night, they were very lucid on the skinny side, but not on the fleshy or 

 inward part; on the 3d, the fleshy or central parts of the fish were thickly covered 

 with a rich azure light ; on the 4th, they continued exceedingly luminous; and on 

 the 5th and 6th they were still lucid. It is surprizing to think what a profusion of 

 light was emitted from the interior substance of this single fish. — Exper. 15. A 

 similar experiment was made with a mackerel, and with similar effects. These 2 

 experiments were frequently repeated. — Exper. 16. But the soft-roe, of both the 

 herring and the mackerel, abounds more with light than even the flesh. When it 

 is in its most luminous state, which generally happens about the 3d or 4th night, 

 it wiH sometimes shine so very splendidly, as to appear like a complete body of 

 light. It is remarkable that the hard-roe in general does not emit so much light 

 as the soft-roe. When the roes were used, they were laid on plates, and deposited 

 in the laboratory. 



Obser. 1. The above experiments clearly prove, as I apprehend, that this light 

 is a constituent principle of marine fishes : and that it is separated, by the men- 

 struum employed on this occasion, in the same way that the principles of any 

 other body are separated, by the menstruum fitted to decompose it. They like- 

 wise show, that it is not partially but wholly incorporated with every part of their 

 substance, and makes a part of it, in the same manner as any other constituent 

 principle. 



Obser. 2. Light is probably the first constituent principle that escapes, after the 

 death of marine fishes. The experiments of the first $. teach us that it appears 

 soon after death, even in fishes which, to the eye, seem quite fresh and sweet ; or 

 at least long before any sensible putrescence takes place. And we have seen that 



