materials again, of a complex nature from the simple carbon compounds so liberated. The close resemblance between animal and vegetable cells is further shown by the fact that many lower plants (bacteria, moulds, &c.) not only flourish in solutions of albumin and sugar, but actually shed out ferments to convert proteid into peptone, and starch into sugar, to aid absorption. They breathe oxygen, produce carbonic acid, amidoderivatives, and, without the aid of sunlight, fat, carbohydrate, and proteid. Nägeli has shown that these fungi will assimilate carbon from compounds in which it is combined with hydrogen (amines, &c.), but not from those in which it is combined with nitrogen (cyanogen, &c.). 4 The question whether light has any influence in accelerating the chemical processes in animals, was answered in the affirmative by Moleschott 2 and v. Platen.3 Speck and Loeb 5 have, however, shown that light of itself does not cause the increased production of carbonic acid, but acts reflexly through the nervous system, especially through the retina, whereby increased muscular movements occur, and so an increase in the chemical processes takes place. Loeb took lepidopterous larvæ in the chrysalis stage when movements are absent, and found that oxidation processes were practically equal in those exposed to light and those kept in the dark. APPENDIX. CHLOROPHYLL The term chlorophyll was invented by Pelletier and Caventon; 7 it is the substance or mixture of substances to which the green colour of leaves and other vegetable organs is due. It is an exceedingly unstable body, and most attempts to isolate it have failed, because in the processes adopted for the purpose decomposition has been brought about. Berzelius, Mulder, and Fremy employed strong mineral acids to extract it from leaves, under the mistaken impression that it was a stable body, but solutions of chlorophyll are destroyed by the action of air and sunlight, much more than by strong acids. 1 Sitzungsb. Bair. Akad. Wiss. 1879. ? Wien. med. Wochensch. 1885. Arch. f. exp. Path. u. Pharmak. xii. 3 Pflüger's Archiv, xi. 272. The following account of the chemistry of chlorophyll is almost entirely an abstract of a paper by Dr. Schunck on that subject in the Annals of Botany, vol. iii. pp. 65–120. Annales de chimie et de physique, ix. 194. Gautier obtained a solution of chlorophyll by the use of neutral solvents, like alcohol and ether, and stated he obtained green crystals which he considered to be composed of the pure pigment, but Hansen2 did not succeed in obtaining them. Hansen employed caustic soda as a solvent; this saponifies the fat which accompanies the chlorophyll. A yellow pigment is removed from the mixture by light petroleum, and then the chlorophyll is dissolved out by a mixture of alcohol and ether. On evaporating the solvent, dark green sphæro-crystals of 'chlorophyll-green' are left. These crystals can, however, hardly be composed of pure chlorophyll, as they are easily soluble in water, a medium in which chlorophyll is insoluble; and in a later communication Hansen himself has admitted that his crystals contain sodium. In view of the difficulty found in isolating chlorophyll, our knowledge of its chemical and physical properties is necessarily limited. It is insoluble in water, and soluble in substances which, like alcohol, ether, carbon disulphide and chloroform, dissolve fats. These solutions show a green colour with a red fluorescence. Spectroscopically a solution shows four distinct bands and two indistinct bands. The two latter, distinguished as bands V and VI, are situated as is seen in figure 51 at the blue end of the spectrum, and are only visible by sunlight in dilute solutions. Some observers consider that these are not true chlorophyll bands, but belong to a yellow colouring matter which accompanies chlorophyll, and which is called xanthophyll. Kraus and Sachsse have partially succeeded in separating the two pigments. Elementary analyses of chlorophyll have yielded most discordant results; two of the latest determinations that have been made will serve to illustrate this statement. Oxygen is also present; when burnt, chlorophyll leaves an ash which contains phosphates of calcium and magnesium and a little ferric oxide. The ash has an acid reaction due to acid phosphate. The phosphates may be derived from phosphorus in the chlorophyll, or in an impurity; there is equal doubt with regard to the iron, whether or not it is con 1 Compt. rend. lxxxix. 861. 2 Arbeiten d. Bot. Inst. Würzburg, iii. 123 and 430. 3 Zur Kentniss d. Chlorophyllfarbstoffe, Stuttgart, 1872. tained in the chlorophyll molecule. Most observers agree in regarding chlorophyll as a substance, the molecules of which are in a state of unstable equilibrium. fresh Decomposition products of chlorophyll. -Hoppe-Seyler1 extracted grass with boiling absolute alcohol; the extract on being allowed to stand, deposited crystals which were purified by recrystallisation ; the substance so obtained, he termed chlorophyllan. It melts at 110°C. to a black liquid, which on further heating burns with a luminous flame. It is easily soluble in ether, light petroleum, benzol, and chloroform. Its solutions show the characteristic first band of chlorophyll, but the remaining bands differ from those seen in fresh plant extracts. Hence it is probably a decomposition product of chlorophyll. Its percentage composition is C, 73·34; H, 9.72; N, 5·68; P, 1·38; Mg, 0.34. On treatment with hot alcoholic potash, it yields a black crystalline acid (chlorophanic acid), glycero-phosphoric acid, and neurine. Hence chorophyllan is probably a lecithin. By the combined action of ether and hydrochloric acid Fremy 2 obtained two pigments from chlorophyll, a yellow and a blue. The yellow pigment dissolved in the ethereal fluid, the blue one in the acid below it. The names phylloxanthine and phyllocyanine were respectively given to these colouring matters. Schunck confirms Fremy's results in the main, and gives a full account of the chemical, physical, and spectroscopic appearances of these two substances in the memoir already referred to. Phyllocyanine is in contrast to chlorophyll very stable; it is a weak base, and forms compounds with zinc, copper and other metals. Phylloxanthine is more difficult to purify than phyllocyanine. It must be carefully distinguished from xanthophyll, to be described later. Whether phylloxanthine is converted into phyllocyanine by the continued action of the acid, or whether the two pigments are formed independently, but in succession, from chlorophyll, or whether lastly the two owe their formation to two distinct substances which together constitute ordinary chlorophyll, must be still considered doubtful. Alkalis cause a decomposition or change in the chlorophyll; Hansen's chlorophyll-green is a product of this kind, and Schunck has obtained a crystalline product he terms phyllotaonin. Alkali first converts chlorophyll into a substance of which chlorophyll-green is the sodium compound; on decomposition with acids this yields phyllotaonin, 1 Zeit. physiol. Chem. iii, 339; iv. 193; v. 75. 2 Comptes rend. 1. 409; lx. 188; lxxxiv. 983. On the subject of the decomposition of chlorophyll by acids see also Filhol, Ibid. lxvi. 1218; lxxix. 612 (who describes a black crystalline substance), Russell and Lapraik, Journ. Chem. Soc. xli. 334 (this deals especially with spectroscopic appearances). which in a nascent state in contact with alcohol and ether undergoes etherification. It has the following percentage composition: C, 66-49 ; H, 6.58; N, 3·32; O, 23.61. Schunck has further described some interesting experiments on the action of aniline on chlorophyll. Substances accompanying chlorophyll.-Berzelius' supposed that the yellow colour of autumn leaves was formed from chlorophyll in consequence of changes induced by cold; he termed it xanthophyll. Kraus endeavoured to show that ordinary chlorophyll is a mixture of two pigments-a bluish one, cyanophyll, and a yellowish one, xanthophyll; and there is good reason to suppose that the xanthophyll of autumn leaves is merely the yellow pigment left after the fading of the blue. It is, however, doubtful if the yellow colouring matter of etiolate leaves, of green leaves, and of autumn leaves is the same. Stokes 2 separated two green and two yellow pigments. Tschirch calls the yellow pigment of etiolate leaves etiolin, and separates it widely from the xanthophylls, of which he describes five. Schunck has found the yellow pigment of faded leaves to consist of two distinct yellow colouring matters, differing in solubilities and in spectroscopic appearances. Of all these substances one only, chrysophyll (Hartsen, the erythrophyll of Bougarel), has been obtained in a pure state. Leaves are extracted with boiling alcohol; the extract on standing deposits red crystals, mixed with fat and chlorophyll; the deposit is dissolved in chloroform, filtered, and alcohol added to the filtrate, crystals again form on standing, and may be obtained pure by repeating the process several times. Solutions of this substance show two bands at the blue end of the spectrum, coinciding very nearly with bands V and VI of the ordinary chlorophyll spectrum. One other xanthophyll, at least, and probably the remainder give no spectroscopic bands. It is perhaps one of the xanthophylls to which is due the glucose reaction observed by Schunck after treating chlorophyll solutions with acids, since the substance is to a great extent removed by agitating the solutions with carbon disulphide, being afterwards found in the brownish-yellow liquid. These substances must all be carefully distinguished from phylloxanthine, a product of decomposition of true chlorophyll. Chlorophyll in animals. The question as to the existence of chlorophyll in animals has been much debated. In attempting a solution of this question, the first error one must guard against is that of looking upon every green pigment as chlorophyll. In Bonellia riridis (a gephyrean worm), the colour is not due to chlorophyll at all, but to a somewhat similar pigment called Bonellein by Sorby. In Phyllodoce 1 Ann. de Pharm. xxi. 261. 5 Ibid. xxxvi. 183. 2 Proc. Roy. Soc. xiii. 144. 2 viridis (one of the polychate worms), P. Geddes' failed to get any evolutions of oxygen on exposing it to sunlight. The reason is that the green pigment present, is not chlorophyll (MacMunn). In other cases the formation of chlorophyll is due to parasitic algæ, existing within the animal organism, and is therefore not the direct product of the latter. There are cases, however, such as Hydra viridis and Spongilla fluviatilis, in which chlorophyll does exist in the cells of the animals themselves (Ray Lankester). MacMunn also has found it in several sea water sponges,3 and in the elytra of cantharides beetles.4 Poulton has found it in the blood of many butterflies and moths, where it is probably derived directly from the food, and is apparently functionless. MacMunn has found a chlorophyll in so-called livers of many invertebrates, which he terms entero-chlorophyll, and which he regards as being respiratory in function. FIG. 51.-Absorption spectra of chlorophyll and its derivatives. i. Chlorophyll, strong solution. ii. The same much diluted to show the bands at the blue end of the spectrum. iii. Solution of phyllocyanin. iv. Solution of phylloxanthin. v. Product obtained by treating phyl'oevanin with caustic alkali, then with acid, or by treating phyllotaonin with acid. vi. Ethyl compound of the preceding. (The above figure is from Dr. Schunck's article Chlorophyll in Watts' Dictionary.) Tests for chlorophyll.-Obtain the pigment in solution and compare its absorption spectrum with that of chlorophyll. Add hydrochloric acid in large amount, and allow the mixture to stand some days; filter off the dark deposit, dissolve some of it in ether, and compare the 1 Proc. Roy. Soc. Edin. xi. (1881-2). 2 Journ. Marine Biol. Ass. 1889, p. 59. 3 Journ. Physiol. ix. 1. Brit. Assoc. Rep. 1883. This confirms the original statement of Pocklington which was called in question by Krukenberg and Chautard. 5 Proc. Roy. Soc. 1885, no. 237. 6 Ibid. xxxv. 370. |