in the intestine of the tadpole. go 7 
the latter becomes of a vivid red ; this, Mr. Hatchett observes, 
is the colouring matter of the shell, which three or four years 
ago, Mr. Branbe found to become red by the application of 
acids without heat; for dilute sulphuric, nitric, muriatic, and 
the strong acetic acids immediately produce the same effect on 
the colouring matter of the spawn, but this is not the case 
when a weak acid, such as common distilled vinegar, is em- 
ployed. 
When this bright red colour has been produced by the 
above acids, it appears to be permanent, excepting when nitric 
acid has been used, for then the red colour changes to yellow, 
which by the affusion of ammonia becomes orange colour, as 
is usual with animal substances so treated. 
Dilute nitric acid in which it had been digested, afforded 
slight traces of a phosphate, which was not phosphate of lime. 
As the red colour is produced by acids as well as by heat, 
there was some reason to expect that it would have been de- 
stroyed, or at least that its intensity would have been dimi- 
nished by a great excess of the alkalies, but not the smallest 
effect was produced by any of these, and indeed so far from 
it, that the recent spawn when put into a solution of caustic 
potash, became in a few seconds changed to as bright a red as 
when the mineral acids had been employed. 
The red colour is also produced by the effects of air, light, 
and the evaporation of moisture, for paper or linen which 
have been stained with the olive coloured substance, become 
red in the course of a few minutes, so that in this respect it 
somcwnat resembles the secretion obtained from the bucci- 
nurn Iapillus,or purple whelk. The purple colour of this last 
does not, however, suffer any change, whilst the colouring 
MDCCCXVI. S S 
