June 29, 1893J 



NA TURE 



211 



monia is precipitated by an aciJ, the coaguluin formed is very 

 voluminous. [The experiment was shown] One gramofturacin 

 is capable of formin:; a semi-solid mass with 5oo grams of water. 

 Another character which turacin shares with many other colloids 

 is its solubility in pure water and its insolubility in the presence 

 of mere traces of saline matter. It would be tedious to enumerate 

 all the observed properties of turacin, but its deportment on 

 being heated, and the action of sulphuric acid upon it, demand 

 , particular attention. 



At too" C, and at considerably higher temperatures, turacin 

 suflfers no change. When, however, it is heated to the boiling., 

 point of mercury it is wholly altered. No vapours are evolved, 

 but the substance becomes black and is no longer soluble in 

 alkaline liquids, nor, when still more strongly heated afterwards 

 can it be! made to yield the purple vapours which unchanged 

 turacin gives off under the same circumstances. This peculiarity 

 of turacin caused great difficulty in its analysis. For these purple 

 vapours contain an organic crystalline compound in which both 

 nitrogen and copper are present, and which resists further de- 

 composition by heat. [Turacin was so heated as to show its 

 purple vapours, and also the green flame with which they burn] 

 This production of a volatile organic compound of copper is 

 perhaps comparable with the formation of nickel and ferro- 

 caibonyl. 



The action of concentrated sulphuric acid upon turacin pre- 

 sents some remarkable features. The pigment dissolves with a 

 fine crimson colour and yields a new compound, the spectrum 

 of which presents a very close resemblance to that of haemato- 

 porphyrin [turacin was dissolved in oil of vitriol ; the spec- 

 trum of an»ammoniacal solution of the turacoporphyrin thus 

 produced was also shown], the product obtained by the same 

 treatment from hsemaiin ; in other respects also this new 

 derivative of turacin, which I call turacoporphyrin, reminds one 

 of haematoporphyrin. But, unlike this derivative of hEematin, it 

 seems to retain some of it.s metallic constituent. The analogy 

 between the two bodies cannot be very close, for if they were 

 so nearly related as might be argued from the spectral observa- 

 tions, haematin ought to contain not more, but less metal than 

 IS found lo be present therein. 



The percentage composition of turacin is probably carbon 

 ;3'69, hydrogen 46, copper 7'oi, nitrogen 6'95, and oxygen 

 2774. These numbers correspond pretty nearly to the em- 

 pirical formula CgaHgiCujN'gOjj ; but I lay no stress upon this 

 expression. 



1 have before said that copper is very widely distributed in 

 the animal kingdom. Dr. Giunii, of Naples, largely extended 

 (i88i) our knowledge on this point. I can hardly doubt that 

 this metal will be found in traces in all animals. But, besides 

 turacin, only one organic copper-compound has been as yet 

 rccoj'nised in animals. This is a respiratory, and not a mere 

 ilccorative pigment like turacin. Leon Fredericq discovered 

 this substance, called hsemocyanin. It has been observed in 

 several genera of Crustacea, Arachnida, Gastropoda, and 

 Cephalopoda. I do not think it has ever been obtained in a 

 stale of purity, and I cannot accept for it the fantastic formula — 

 CsBjHjjjjCuSjOjsg — which has recently been assigned to it. 

 On the other hand, I do not sympathise with the doubts as to 

 iis nature which F. Helm has recently formulated in the Comptis 

 A't ndus. 



It is noteworthy in connection with the periodic law that all 

 t lie essential elements of animal and vegetable organic com- 

 pounds have rather low atomic weights, iron, manganese, and 

 copper representing the superior limit. Perhaps natural organic 

 compounds containing manganese will some day be isolated, 

 I but at present such bodies are limited to a few containing iron, 

 and to two — hsemocyanin and turacin — of which copper forms 

 an essential part. 



ir I have not yet unravelled the whole mystery of the occur- 

 tcnce and properties of this strange pigment, it must be remem- 

 bered that it is very rare and costly, and withal difficult to 

 (irxpare in a state of assured purity. It belongs, moreover, to a 

 cl.i" of bodies which my late master. Dr. A. W. von Hofmann, 

 ,(|"alnily designated as "dirts" (a magnificent dirt, truly!) — 

 isub.-.tances which refuse to crystallise, and cannot be distilled. 

 I have experienced likewise during the course of this investi- 

 gation, frequent reminders of another definition propounded by 

 the same great chemist when he described organic research as 

 " a more or less circuitous route to the sink " ! 



1 am very glad to have had the opportunity of sharing with 

 an audience in this ins'ilution the few glimpses I have caught 



from time to time during the progress of a tedious and still in- 

 complete research into the nature of a pigment which presents 

 physiological and chemical problems of high, if not of unique, 

 interest. 



Let my last word be a word of thanks. I am indebted to 

 several friends for aid in this investigation, and particularly to 

 Dr. MacMunn, of Wolverhampton, the recognised expert in the 

 spectroscopy of animal pigments. 



ARTIFICIAL IMMUNITY AND TYPHOID 

 FE VER. 



'T'HE announcement by Metchnikoflf of his beautiful theory ol 

 the " mechanism," as it were, of immunity, which he con- 

 ceives as dependent upon the activity of the phagocytes or 

 migratory cells of the body in the presence of disease germs, 

 has called forth an immense number of researches in this direc- 

 tion from all parts of the world. But whilst some bacteriologists 

 are engaged upon studying critically the experimental evidence 

 which can be adduced in support of this theory, others are 

 busy with the practical side of the subject and are devoting 

 themselves to the investigation of what substances are capable 

 of conferring immunity upon animals towards any particular 

 disease, and hardly a month passes without some contribution 

 being made to this important inquiry. The great discovery 

 made by Behring that the blood serum of animals rendered 

 artificially immune against a particular di^ease will, on being 

 introduced into other animals, protect them from an attack of 

 that particular disease, has been confirmed in the case of tetanus 

 or lockjaw by Behring and Kitasato, and as regards diphtheria 

 by Behring. In a more recent contribution Brieger, Kitasato, 

 and Wassermann ("Ueber Immunilat und Giftfestigung," 

 Zritschrift fiir Hygiene, vol. xii. 1892) have, amongst other 

 investigations, succeeded in protecting and healing mice from the 

 evil effects of inoculations with the typhoid bacillus by the 

 introduction of serum obtained from a guinea-pig immune 

 against typhoid. The further study of immunity with reference 

 to this disease is the subject of two elaborate memoirs in the 

 A nnahs dt r Institut Pasteur, November, 1892, by Sanartlli in 

 Siena, and Chantemesse and Widal in Paris, and the ground 

 covered by these two investigations is to a great extent identical. 

 Sanarelli selected guinea-pigs as the subjects for his experiments, 

 these animals being, as is well known, more difficult to protect 

 from the fatal results of typhoid inoculations than mice. He 

 states that if O'S c.c. of therapeutic serum be simultaneously 

 introduced with an otherwise fatal dose of a typhoid culture, 

 these animals without exception develop no typhoid symptoms, 

 whilst guinea-pigs inoculated with an equally fatal dose of 

 typhoid, but without the curative serum, invariably die. 

 Chantemesse and Widal have pursued the inquiry still further, 

 and have investigated the properties of serum taken from normal 

 animals — that is to say, from animals which have not been 

 infected with or rendered artificially immune from typhoid. In- 

 vestigations similar to those made previously by Stern have also 

 been conducted with human serum obtained from patients who 

 have recovered from typhoid fever and also from those who 

 have never been attacked by this malady. 



Chantemesse and Widal state that whereas the serum derived 

 from typhoid patients and from immune animals invariably con- 

 fers protection upon infected animals, that obtained from 

 normal animals and from people who have never had typhoid, 

 only exceptionally exercises any curative power. These authors 

 have also compared the degree of immunity induced in animals 

 by the inoculation of curative serum and sterilised cultures of 

 the typhoid bacillus respectively. This latter process is another 

 method of protecting animals against infection, and was resorted 

 to before the experiments with serum were made. It was found 

 that whilst the serum acts rapidly, and confers immunity when 

 administered in small quantities, its protective power only ex- 

 tends over a short period of time, apparently disappearing in less 

 than a month. The sterilised typhoid cultures on the other hand, 

 although working more slowly and requiring to be introduced in 

 larger doses than the serum, endow the animal with immunity 

 over a longer space of time, animals having been found immune 

 even afier the lapse of two months. Finally, attempts were made 

 to arrest the progress of typhoid fever in people by the inocula- 

 tion of therapeutic serum obtained from guinea pigs. So far, 

 however, these investigations have not been .successful, and if it 

 be remembered that one point of cardinal importance in the 



NO. 1235, VOL. 48] 



