April 14, 1 881] 



NATURE 



561 



as that of the lens forwards. By the time the lens 

 reaches the edge of the danger-arc the screen will have 

 been pushed to the top of the inclined plane, and the full 

 beam of light coming from the now entirely uncovered 

 lens will be pointing in the required line of cut-off which 

 is the border of the danger-arc. But whenever the 

 further revolution of the apparatus causes the snug to 

 pass clear of the edge of the screen so as to free it 

 from pressure, it will immediately run back again to its 

 original position in front of the lens, so as to prevent any 

 light being now sent forwards. If that light were not at 

 once intercepted part of it would, by the movement of the 

 frame, begin to pass across the line of cut-off, so as to be 

 seen within the danger-arc. By this continued recipro- 

 cative movement of the screen as lens after lens comes 

 round, the same effect will be successively produced, and 

 the light will always be cut off in the line of obscuration 

 as sharply as in the case of a fixed light, so that the 

 flashes will never be seen within the danger-arc. 



In cases where the light has to be cut off on both sides 

 of a danger-arc a similar reciprocating screen is as 

 applicable to the lenses when passing out as when passing 

 into the danger-arc. But in this case the lens, on leaving 

 the danger-arc, will take the screen round with it up an 

 inclined plane until the a.xis of the lens is parallel to the 

 line of cut-off, when the screen will recoil and the light 

 become visible with full power in the line of cut-off. 



.A small spherical mask placed inside of the apparatus 

 may be made to produce the same effect by reciprocating 

 between the lenses and the flame. When the danger-arc 

 is of small amplitude the screens, which must always be 

 as broad as the lens, might come in the way of the light 

 passing over the safety-arcs. To obviate this, cloth curtains 

 might be made to wind up on vertical rollers similar in 

 construction to those used for ordinary house- blinds. 



THO^rAS Stevensox 



CHLOROPHYLL ' 



AN account was given in Nature, vol. xxi., p. 8;, 

 of Prof. Pringsheim's first publication on this sub- 

 ject. He had then found that exposure to intense light 

 for a few minutes causes the chlorophyll-corpuscles con- 

 tained in the cells of plants to lose their green colour ; he 

 also pointed out that this effect is produced not by heat 

 but by light, and only in the presence of oxygen, and 

 further, that the highly refrangible rays of the spectrum 

 are those which are principally concerned in it. He also 

 announced the discovery in the chlorophyll-corpuscles of 

 a substance termed Hypochlorin. 



The paper now under consideration gives a full account 

 of all the observations and experiments which he has 

 made up to the present time, and he considers that they 

 tend to confirm the conclusions at which he had previously 

 arrived. It will be well, before entering upon a discus- 

 sion of the very difficult questions which are raised, briefly 

 to enumerate the principal new facts which he now brings 

 forward. 



In the first place, he is able to throw some light upon 

 the intimate structure of chlorophyll-corpuscles by means 

 of a new method for investigating them. This method 

 consists in treating them with a dilute acid {e.g. i vol. of 

 glacial acetic acid to 2 of water, or i vol. of picric acid 

 to 3-6 of water, or i vol. of sulphuric acid to 20-40 of 

 water, or i vol. of strong hydrochloric acid to 4. of water), 

 or warming them in water, or exposing them to the action 

 of steam. The effect of this treatment is to cause the 

 escape of the chlorophyll from the corpuscle, together with 

 certain fluid or semi-fluid substances which accompany it, 

 in the form of viscid drops, leaving the ground-substance 

 of the corpuscle as a colourless, apparently protoplasmic, 

 hollow sphere, with a much perforated wall. 



^ "Untersuchungen iiber Llchtwirkung und Chlorophyllfunction in der 

 Pflanie," by Prof. X. Pringsheim (.JaJirlniciur/ur IViss. Bol., Ed. XII., 

 Heft 3 : Leipiig, i83i). 



These viscid green drops, when produced by the action 

 of warm water or of steam, appear to consist of an oil 

 which holds the chlorophyll and other substances in 

 solution. When they are produced by means of a dilute 

 acid, they appear to contain a substance which is not 

 present when they are extracted by warm water or by steam. 

 Certain dark brown masses make their appearance which 

 are of a tolerably firm consistence and of varying form. 

 These gradually become harder, and assume a crystal- 

 loidal appearance, probably, as Prof. Pringsheim suggests, 

 in consequence of a conversion into resin of the oily 

 matter which is present ; but it is by no means the whole 

 of the substance which thus solidifies, but only a certain 

 constituent of it. The colour of the mass is doubtless due 

 to the presence of altered chlorophyll, and this may affect 

 even the crystalloids, but they may be obtained colourless. 

 It is to the substance which assumes the crystalloidal 

 form, or rather to some substance pre-existent in the 

 chlorophyll-corpuscle from which these crystalloids are 

 derived by the action of the acid, that Prof. Pringsheim 

 gives the name of Hypochlorin. 



He meets the doubts that may arise as to the chemical 

 individuality of this substance, as also the suggestion that 

 it may be a product of the alteration of the chlorophyll, 

 by pointing out that it cannot usually be obtained at any 

 one time from all the corpuscles of a given cell. It is 

 therefore a substance which, as it is present in some and 

 not in others, cannot be derived from chlorophyll which 

 is present in them all, and which probably bears sonie 

 definite relation to the metabolic processes going on in 

 the corpuscles. 



Since no hypochlorin can be obtained from cells 

 which ha\ e been warmed in water or acted upon by steam, 

 it appears that this substance is decomposed by heat. 



After giving a detailed description of the arrangement 

 of the apparatus used in his observations. Prof. Prings- 

 heim goes on to give an account of the eft'ects produced 

 by exposure to intense fight in the different parts of which 

 the cell consists. He again insists that none of the 

 following phenomena can be the result* of excessive 

 heating of the object, for he found that cells not containing 

 chlorophyll {e.g: colourless zoospores,/ could bear the ex- 

 posure for half-an-hour without injury, and further, that the 

 phenomena were produced more readily by blue or green 

 light than by red light which has a much greater heating 

 effect. The principal phenomena obser\^ed are as 

 follows : — 



1. The colouring-matter. 



The chlorophyll-corpuscles lose their colour in a few- 

 minutes, but this' does not take place when oxygen is not 

 present, nor in red light. There is no trace of chlorophyll 

 left in the corpuscles. Prof Pringsheim is therefore of 

 opinion that its decolorisation is a phenomenon of oxida- 

 tion, and that the products are gases. Further, this dis- 

 appearance of the chlorophyll is not prevented by the 

 absence of carbonic acid gas. The corpuscles which have 

 lost their green colour do not regain it, although the cell 

 in which thev are contained, still continues to live ; on 

 this account Prof. Pringsheim regards the decompo- 

 sition of chlorophyll as a pathological and not as a 

 normal process. 



Colouring matters, other than chlorophyll, which occur 

 in the cells of plants, are likewise decomposed, but not 

 all of them. Thus, the blue pigment of the Phycochro- 

 maceae, the brown of Fucus, the red of the Florideae, the 

 orange of the corolla of Calendula, the blue in the cells 

 of the staminal hairs of J radescantia virginica, dis- 

 appear, but the blue pigment in various flowers is not 

 decomposed by exposure to intense light. 



2. The ground-substance of the chlorophyll-corpuscles 

 and their contents. 



If a cell of Nitella or of Spirogyra be kdled by the 

 action of heat, for instance, the chlorophyll-corpuscles of 

 the one and the spiral band of the other will absorb water 



