Miscellaneous. 389 



the granule, — not often, perhaps only once in a thousand times; yet, 

 as far as I am aware, no such occurrence has ever been observed. 



With regard to the observed existence of a membrane, of which I 

 have not yet spoken, the experiment of Mr. Busk, and also that of 

 merely boiling a little starch in water, and examining the results, are, 

 to my mind, quite conclusive. In the latter case we observe nume- 

 rous thin, collapsed, vesicular-looking membranes, which do not 

 appear to dissolve after many hours' boiling, while the true starch 

 which these membranes enclose is extracted by the water, as is proved 

 by its behaviour with iodine. This membrane appears to me to differ, 

 not only in consistence, but also in chemical character, from starch, 

 since, if iodine be added to starch which has been boiled in water, 

 and the result examined by the microscope, the blue colour is seen 

 to be due to amorphous masses of starch, — the membranes, when seen 

 separate from the starch, not appearing coloured. 



The coloration was produced in some cases by portions of yet ad- 

 hering starch, which of course was coloured blue. This might, how- 

 ever, be distinguished from a true coloration of the membrane by its 

 patchy granular appearance, and also by the colour not being thicker 

 where wrinkles were visible in the membrane. A large quantity of 

 iodine was required to produce any particular effect ; the membranes 

 then became of a deep brownish-red, but not blue, which certainly 

 appears to evidence a different composition from starch. At first 

 I was inclined to believe the enveloping membrane to differ from cel- 

 lulose, not being able to produce a blue colour with iodine and sul- 

 phuric acid. I have since succeeded in producing this effect by mace- 

 rating boiled starch in dilute nitric acid for several hours. Schleiden 

 has observed that the outer layer of the starch granule behaves dif- 

 ferently with iodine from the rest, and explains it by saying that the 

 outer layer becomes infiltrated with foreign matters, which hinder the 

 characteristic reaction of starch. This is in all probability correct, 

 but it is inconsistent with his own theory. The outer membrane of 

 the small round granules is affected precisely as that of the larger ; 

 yet, according to his views, the small granules were the nuclei, so to 

 speak, on which the larger were to be deposited. Each layer in suc- 

 cession ought to be infiltrated, but evidently is not. His explanation, 

 in fact, is an argument in favour of my view. The membrane, being 

 always exterior, of course runs much greater chance of infiltration. I 

 have not yet said anything of the concentric lines, my theory not 

 being inconsistent with either of the views entertained on the subject. 

 Although I believe in the existence of a membrane, I do not see that 

 the lines must necessarily arise from foldings of that membrane. 

 They may still be due to the existence of layers. Schleiden states 

 that the concentric lines may be traced all round the granule. I 

 have not been able to satisfy myself of this, and am inclined to 

 believe that only the interior lines can be traced entirely round. If 

 starch be heated on a metal plate until it turns brown, then treated 

 with weak solution of iodine and examined, crescentically-shaped 

 pieces appear to separate from the large end of the granule, leaving a 



