86 



NATURE 



[Nov. 2-j, 1879 



of the fat or starch in the blanched cell, nor the formation 

 of grape-sugar or dextrin : he therefore concludes that 

 the products of the oxidation of the chlorophyll are given 

 off in the gaseous form. In the second place he concludes 

 that the changes produced in the protoplasmic cell-contents 

 are the direct effects of the photochemical action of light. 

 That they are not due to the presence of the products of 

 the decomposed chlorophyll is shown by the fact that they 

 may be observed equally well in cells which do not contain 

 chlorophyll, such as the stinging-hairs of the nettle, &e. 

 This being the case, he infers that they too are produced 

 by a process of combustion. The final conclusion to 

 which he comes is that chlorophyll exercises a protective 

 influence over the protoplasmic cell-contents by absorbing 

 the actinic rays of the spectrum, thus diminishing the 

 combustion (respiration) going on in the cell ; that it is in 

 fact the regulator of the respiration. 



In another series of experiments Prof. Pringsheim 

 endeavours to determine what are the substances which 

 become oxidised in the process of respiration. He finds 

 in all chlorophyll-containing cells, a substance which can 

 be best extracted by immersing the parts — leaves for 

 instance — in dilute hydrochloric acid for several hours. 

 This substance, to which he gives the name of hypo- 

 chlorin or hypochromyl, is of an oily nature ; it is pro- 

 bably a hydrocarbon which consists only of carbon and 

 of hydrogen, or one which contains oxygen also in its 

 molecule, but in smaller proportion than the carbo- 

 hydrates ; it is soluble in alcohol, ether, turpentine, and 

 benzol, but insoluble in water and in solutions of neutral 

 salts ; it occurs in long, red-brown, crystalline needles 

 which soon harden after extraction, into an imperfectly 

 crystalline mass of resinous or waxy consistence. It is 

 readily oxidisable, as is shown by the fact that it dis- 

 appears from the cell on exposure to intense light in an 

 atmosphere containing oxygen, even sooner than the 

 chlorophyll. Prof. Pringsheim is of opinion that this 

 substance is the first product of the assimilation of the 

 chlorophyll-corpuscle, and that starch and oil are sub- 

 sequently formed from it by oxidation. 



Applying these views to the life of the cell under 

 ordinary conditions, the changes going on in the cell 

 when exposed in the air to sunlight would be somewhat 

 as follows : the general protoplasm would undergo some 

 amount of oxidation, but not so much as to materially 

 diminish its quantity or affect its properties ; in the 

 chlorophyll-corpuscles, oxidation would be either entirely 

 arrested in consequence of the absorption of the actinic 

 rays by the green colouring-matter, or at least so much 

 diminished that the synthesis of the elements of water 

 and carbonic acid to form hypochlorin could take 

 place. 



Since this paper is stated to be a merely provisional 

 account of these very interesting experiments, it is 

 hardly fair to submit it to a detailed criticism : it will be 

 better to wait until the publication of the more complete 

 account which Prof. Pringsheim promises in an early 

 number of his Jahrbikher. All that will be attempted 

 at present is to indicate some of the principal difficulties 

 which beset the acceptance of these new views. For 

 instance, exception may be taken to the view that chloro- 

 phyll, when exposed to intense light is oxidised into 

 gaseous bodies. It is well known that an alcoholic 

 solution of chlorophyll, when exposed to sunlight in the 

 presence of air, becomes oxidised and assumes a pale 

 yellow colour ; it may be that this also takes place in the 

 chlorophyll-corpuscles, the yellow colour being hardly 

 distinguishable on account of the smallness of the quantitv 

 which is present. Again, it will doubtless have occurred 

 to every reader of this paper that hypochlorin may be 

 nothing more than the wax which has long been known 

 to exist in considerable quantity in chlorophyll-corpuscles. 

 But the main difficulty has reference to the protective 

 functions which Prof. Pringsheim ascribes to chlorophyll. 



Admitting that the changes described above as occurring 

 in the protoplasmic cell-contents are really the results of 

 excessive oxidation consequent upon exposure to the 

 intense light, it is evident that they are effected less 

 quickly than the oxidation of the chlorophyll itself; that 

 is to say that, ceteris paribus, the chlorophyll is more 

 readily oxidised than the protoplasm. This being the 

 case, it is not easy to understand how the former can 

 efficiently protect the latter from the oxidising influence 

 of light and regulate its respiration. This difficulty might 

 perhaps be met by the suggestion that fresh supplies of 

 chlorophyll are continually being formed, but we have no 

 knowledge yet at present of any such continual formation 

 of chlorophyll ; on the contrary, it is a well-established 

 fact that when once the chlorophyll of a corpuscle is 

 oxidised, it does not regain its green colour. 



It might perhaps be possible to obtain some further 

 knowledge on this subject by observing the effects pro- 

 duced in cells by the action of strong light falling upon 

 them, in some cases, directly, in others, after having 

 passed through a solution of chlorophyll which would be 

 renewed from time to time if necessary. If it were 

 found, that, in the latter case, the cells remained unin- 

 jured whereas in the former they soon died, some im- 

 portant evidence in favour of Prof. Pringsheim's views 

 would be obtained. It might then be possible to extend 

 these experiments and to bring about the formation of 

 starch from carbonic acid and water in the cells of fungi, 

 and even of animals, for Mr. Geddes' interesting obser- 

 vations on planarians show that animal as well as vege- 

 table protoplasm is capable of effecting this synthesis. 

 Sydney H. Vines 



THE CAMBRIDGE NATURAL SCIENCES 



TRIPOS 



AX70ULD science suffer by the division of the second 



*" part of the tripos into a non-biological and a 



biological division which might be taken in successive 



weeks with separate examiners ? 



Let us make sure that in future geologists know well 

 their chemistry and physics, and insist on all biologists 

 knowing how to work their microscope well. Perhaps 

 some geologists will shrink from a division of subjects - r 

 and consider that every geologist should know palaeon- 

 tology well. But the study of fossil plants and animals 

 is surely a part of systematic botany and zoology ; in fact, 

 geology and palaeontology would gain by being separated, 

 so far as the one is physical, stratigraphical, penological, 

 and mineralogical, or the other truly biological. The 

 knowledge of fossils as characterising a " formation " is 

 not a biological subject ; a man may recognise fossils well 

 enough for geological purposes who knows little of zoology 

 properly so called. Biology suffers greatly from the want of 

 palaeontologists as distinct from physical geologists and 

 petrologists. How many men are there who would agree 

 that biology (" the study of things living or that have 

 lived") is very difficult to separate from physical and 

 non-biological subjects for examinational purposes ? Let 

 us acknowledge that it is more necessary that, at the 

 commencement of his scientific career, a man should be 

 known and recognised as a well-educated biologist than 

 as a vegetable anatomist, or a palaeontologist, or an 

 embryologist. Every man seeking biological honours 

 may find sufficiently little chemistry and physics in the 

 first part of the natural sciences tripos not to daunt him, 

 if he is capable of research. Surely it is better to secure 

 a man's general physico-chemical knowledge if he is to 

 be a geological surveyor of the first rank, and also train 

 him in elementary biology, than to encourage too early 

 specialisation. 



My proposal is that in the second part of the natural 

 sciences tripos four or more examiners should be specially 

 chosen to set and approve the biological questions, and 



