November i, 1900] 



NATURE 



17 



of light, separate phlogiston from the tainted air, and repristinate 

 in the atmosphere the power of generating heat by combustion 

 or by respiration. A cycle of the principles of heat and of phlo- 

 giston is thus maintained through atmospheric air between the 

 vegetable and animal kingdoms. Substituting the old concep- 

 tion of phlogiston by the modern idea of energy, we perceive in 

 Crawford's theory the germ of the theory of the preservation and 

 transformation of energy. Crawford's work prepared the way, 

 as Carradori pointed out in 1792, to Lavoisier's experiments on 

 re-piration, and for the ready acceptance of his theory. 



In Italy, where the experiments of Marsiglio Landriani, of 

 Pietro Moscati and of Lazzaro Spallanzani, were then showing 

 the influence of different gases on cutaneous respiration, and 

 where Spallanzani was demonstrating the evolution of fixed air 

 even from tissues separated from the living body, and in 

 organisms prevented from absorbing free vital air, the theory of 

 Crawford was readily accepted, and served as a starling-point to 

 the experiments of Michele Rosa in Modena. Rosa, indeed, 

 followed directly in the track opened by Ludovico Barbieri a 

 century before. By a numerous series of experiments in trans- 

 ferring arterial blood into animals prepared by copious bleeding, 

 and by the different comportment of arterial and venous blood in 

 vacuo, Rosa showed that the vital principle has its seat chiefly 

 in the blood, and is maintained by the continuous action of 

 atmospheric air during respiration, being due to the same cause 

 that maintains combustion. Rosa's work has not been suffi- 

 ciently appreciated because of his misapplication of names, and 

 was too soon forgotten in the great light shed by the experi- 

 ments of Lavoisier ; but there is no doubt that to Rosa is due 

 the first demonstration of the incorporation of oxygen in the 

 blood, of the special labile condition of its combination, and of 

 the supreme importance of aeration for the vitality of all animal 

 tissues.^ 



When Cirillo wrote his essays, the theories of Crawford and 

 of Rosa were in their bloom, and were warmly espoused by the 

 Neapolitan naturalist. Cirillo believed that all life, animal 

 and vegetable, had its origin in the action of air upon the 

 " glutinous principle," that is, the basis of life in all tissues, and 

 that light, electricity and heat, but especially solar light, are all 

 connected with the quickening of life. Like Lavoisier, Cirillo 

 looked upon sunlight as the origin of all life : "Sunlight," he 

 wrote, " the only, the inexhau.stible, primitive and incompre- 

 hensible fount that pours heat and motion and life upon our 

 globe." 



John Hill, in his letter to Linnaeus in 1753, had shown the 

 special connection of light, independently of heat, with the 

 sleep-movements of plants. Priestley's celebrated experiments 

 on the purifying action of vegetation upon air vitiated by respira- 

 tion, or by combustion, had been known since 1772. In 1779 

 Ingen-Housz pointed out that this action of plant-life is due to 

 sunlight, and only takes place when light acts upon green 

 plants. Cirillo himself must have observed the attraction of 

 lower organisms towards light, similar to those swarm-spore 

 movements that shortly after were first described by Cjiuseppe 

 Olivi.2 "Why," asks Cirillo, "do all polyps love light, so 

 that, on darkening the vase in which they are contained, 

 leaving free only a tiny hole, they all forsake darkness, and 

 throng near the spot where they can enjoy the immediate 

 action of the solar rays? Why are all marine animals .so filled 

 with a luminous vapour, emitting phosphoric light ? Why are 

 the most irritable fish phosphorescent and electric ? Why do 

 plants, when deprived of solar light, lose colour, aroma and 

 robustness ? " Cirillo, like most of the writers of his time, was 

 not clear in the distinction between light and heat ; but what 

 is predominant in his mind is that all movement, both in animals 

 and in plants, is due to fixation of vital air, to oxidation, and 

 that light therefore, by causing the sleep-movements in plants, 

 must be connected with some process of oxidation. 



While Cirillo was writing, Senebier had already shown (1788) 

 that the chief action of light in plants is the reverse of oxida- 

 tion, causing the decomposition of carbonic acid and the evolu- 

 tion of oxygen. The importance of this discovery, and the 



1 Michele Rosa, " Letterefisiologiche." sda ed. ; " CoUe osservazioni ed 

 Esperienze sul Sangue fluido e rappreso dal Signer Pietro Moscati," 2 voLs. 

 (Napoli, 1788). 



This edition is dedicated to Domenico Cirillo. The experiments of Rosa 

 were first published in Vicenza in 1782. The experiments of Lavoisier on 

 animal respiration, first published in Paris in 1777, appeared in Italian in 

 1781 (Opuscoli Sceltiiv. 1781, p. 135). 



2 Giuseppe Olivi, " Delle Conferve irritabili, e del lore movimento di 

 progressione verso la luce, Esame chimico" {Metn. di Mat. e Fisica della 

 Soc. Italiana, tom. vi. Venezia, 1793). 



mistaken notions about plant-respiration, caused what may be 

 called the minor functions of light in plants to be neglected. 

 Only long after the days of Cirillo and of Senebier, in the latter 

 part of our century, investigations began on the influence of 

 light in respiratory processes : in the decomposition of chloro- 

 phyll, in changing the composition of the sap, and the distri- 

 bution of osmotic tension, and consequently in causing the 

 movement of plant-organs, as in the case of nyctitropic and 

 heliotropic movements. These changes are promoted, as was, 

 first shown by Michelangelo Poggioli in 1817, by the more 

 refrangible rays of the spectrum, by those rays, namely, 

 that are specially active in causing the oxidation of organic 

 compounds and in decomposing silver and other salts. 



Cirillo's opinions on the chemical activity of solar rays were 

 due to his own original observations on the chemical action of 

 sunlight upon silver chloride. His experiments were made to 

 test the truth of an assertion by Nicola Andria that certain 

 Ischia waters contained phlogisticated alkali (yellow prussiate), 

 and could consequently produce Prussian blue.^ " A curious 

 phenomenon," Cirillo writes, " has been recently observed by 

 me whilst analysing the Oimitello water of the Island of Ischia. 

 Investigations of our chemists had brought them to believe that 

 this water contained a phlogisticated alkali, similar to that pre- 

 pared from the colouring matter of Berlin blue ; for, on mixing 

 the water with some Itina cornea, or with a solution of silver in 

 nitrous acid, not only was a white substance instantly produced, 

 but after a short time it changed to a very beautiful and dark 

 azure colour. This experiment, seeming to show the existence 

 of a phlogisticated alkali in the Oimitello water, having been 

 accidentally repeated by me towards evening, I observed that 

 the mixture remained white during the whole night, becoming 

 azure only on the following morning, after the rising of the sun. 

 I also noted that the intensity of the azure colour in the sediment 

 increased with the growing intensity of sunlight. These results 

 led me to repeat the experiment while excluding all action of 

 light. To half a glass of Oimitello water I therefore added a 

 few drops of the solution of silver in nitrous acid ; and as 

 soon as the white precipitate due to the alkali was formed, 

 I shut the glass in a place utterly impenetrable to light. 

 For many days the precipitate remained white ; but on exposure 

 to light it became cerulean in a few minutes. The same change 

 was observed in a water from Calabria ; for, on treating it as 

 the Oimitello water, it also rendered blue the luna cornea. Also 

 our common waters, probably charged with an alkaline earth, 

 undergo the same change. I am aware of what recent writers 

 have said about the repristination of metals by solar heat ; nor 

 do I ignore how with a burning lens the illustrious Priestley, 

 heating inflammable air in contact with minium inside a glass 

 vessel, was able to repristinate lead. But my experiment will 

 serve at least to correct the error of those who analysed the 

 Oimitello water, believing it to contain a phlogisticated alkali, 

 similar to the Prussian alkali ; and secondly, this experiment 

 gives us a sure proof of the energy of solar rays in repristinating 

 metals. These observations, although having a distant connec- 

 tion with the movements and irritability of vegetables, are also 

 worthy of record in connection with other considerations which 

 I hope shortly to publish." 



Cirillo's es.say was published, in its first edition, in 1789, so 

 that the Oimitello experiments must have been made shortly 

 before that year and after Andria's last publication of 1783. As 

 is well known, the experiments of Scheele (not counting the 

 earlier, forgotten experiments of J. H. Schultze in 1727) were 

 published in Swedish in 1777 ; a French translation, by Baron 

 Dietrich, of Scheele's treatise on Air and Fire appeared m Paris 

 in 1781." Scheele's experimentson luna cornea and other silver 

 salts are quoted and commented upon by Felice Fontana in 

 1783.3 Senebier, in 1782, had been experimenting on the 

 rapidity of action of diflferent lights upon silver chloride.* 

 Cirillo therefore ought to have been acquainted with Scheele's 

 experiments, although there is every reason to believe that he, 

 generally so precise in recording previous work, was not aware 

 that, only a few years before his own experiments with the 

 Ischia water, the action of light upon silver salts, and especially 



1 Nicola Andria, " Trattato delle acque minerali," 2da ediz. (Napoli, 

 1783). 



i Ch. Giul. Scheele, " Traiti chymique de I'air et du feu." Trad. 

 Dietrich. (Paris, 1781). 



3 Felice Fontana, " Sopra la Luce, la Fiamma, il Galore, ed il Flogisto " 

 (Opusc. Scelti vi. 1783). 



^ Jean Senebier, " M(im. physico-chymiques sur I'influence de laLumiere 

 Solaire, pour modifier les etres des trois regnes de la Nature " (Geneve, 

 1782). 



NO. 16 18, VOL. 63] 



