366 M. Caventou's Chemical Researches on Starch, 



manner, and he always obtained the same result. Such a fact 

 gave too rude a blow to the principal idea of the author for 

 him not to verify it in every way : he had also recourse to his 

 microscope, which enabled him to perceive in the gummy li- 

 quid a great number of integuments ; and as these are the cause 

 of the colouration, the fact, contradictory in appearance, was 

 found quite natural ; and it even offered to the author an ad- 

 ditional motive to persist in his view. We then find M. 

 Raspail convinced that the integumentary part alone becomes 

 blue by iodine, and that if the gummy part partakes of this 

 property, it is by means of this last drawn through the pores of 

 the filter. 



With regard to this, I shall observe, that if things took place 

 thus, the blue colouring by iodine ought to decrease in the li- 

 quor with the number of the integuments. 



And yet M. Raspail says : that since the microscope only 

 indicated to him at the most the presence of one integument in 

 a square inch, he had only to pour some iodine in his liquid, 

 and it became quite as blue as with the fecula itself: it is neces- 

 sary then to conclude from it, as appears to me, that there is 

 in empois a substance which becomes blue by iodine, indepen- 

 dently of the integuments. 



The author had this thought, for he could not reject the 

 facts of which he was himself a witness. Moreover, a few 

 lines lower, he admits that the gummy part may also be- 

 come blue by iodine when it is in solution, and he attributes 

 it to the formation of membranes in the liquor, which disap- 

 pear as the blue colour is effaced. 



What is to be concluded from this fact, says M. Raspail ? 

 That the fecula does not become coloured by iodine except 

 when it is in a membranous form. It is on this account that 

 the integuments always remain coloured. 



Thus, according to M. Raspail himself, here is the gummy 

 part which approaches singularly, by its nature, to the integu- 

 ments, since this is as suceptible as them of taking, even in 

 a state of solution, a membranous form, which then permits it 

 to take a blue colour with iodine. But since, in spite of the 

 most careful filtrations of these gummy liquors, the micro- 

 scope has always indicated the presence of some integuments, 

 and since these always remain coloured, how is it that these 

 liquors lose, at the end of twelve or fifteen hours contact 

 with the air, their blue colour, which they regain by the ad- 

 dition of a new dose of iodine ? The integuments then would 

 not always remain coloured, in the same manner as the sup- 

 posed gummy part. It appears to me very difficult to recon- 

 cile all these facts in the manner of M. Raspail. 



To 



