process. The mixture of air and ammonia was filtered through cotton-wool, as it was found that dust impaired the activity of the platinum catalyst. The latter took the form of platinum gauze, throngh which the mixture of ammonia and air was forced, only 1/1000 of a second being occupied in the passing, while the yield amounted to no less than 97 per cent. B. Sc., 2nd Hons. Chemistry (London). 22, ex-Army, just completed Degree from College, desires Post with good prospects in Research or Works Laboratory. Good refer. ences. Details and salary offered to Stubbings, Fair Oak, Eastleigh, Hants. They had many difficulties Chemist, with high qualifications (Ph D., to contend with; one, a minor detail, was that this process produced an extremely penetrating whistling sound. He humorously mentioned how they received one day a visit from a mechanic, who stated that he had not yet encountered any trouble he could not settle with a spanner, and they also received a postcard with the query, Why don't you oil the d-d thing?" Originally, to make one ton of T.N.T. required 1.27 tons of nitric acid, the average for the country; but by the introduction of devices for the recovery of nitrous fumes they succeeded in reducing the amount of nitric acid required to only 0.95 ton in 1918, shortly before the armistice. The necessity of observing the strictest economy with the sodium nitrate supplied made the recovery of the nitrous fumes evolved in the course of producing T.N.T. a very important factor, and Prof. Walker demonstrated by slides the methods used in realising a recovery amounting to 93 per cent nitric acid from the fumes produced in the course of nitration. In conclusion, he remarked that Ph.Ch.) and large experience as Analytical and Pharmaceutical Chemist, speaking many languages, w nts Situation in London. Apply to P. G., Strand Palace Hotel (Room No. 885), 371, Strand, London, W.C. 2. academic chemists had done well in the war, and bad The Council give notice that they will proceed shown that they could enter the manufacturing branch of chemistry if endowed with common sense, and were willing to listen to those who had practical experience and engineering knowledge. The chemist who had a sound knowledge of his profession would also possess the necessary business instinct, and the research laboratories of the Germans were not so much scientific, but rather an indi cation of excellent business methods, implying a co-ordi nation of both aspects of the chemical industry.-Chemist and Druggist.. MEETINGS FOR THE WEEK Saturday, January 3. Royal Institution, 3. (Christmas Lectures). "The World of Sound," by Prof. W. H. Bragg. Monday, January 5. Society of Chemical Industry, 8. Valleys," by Prof. J. W. Gregory. British Psychlogical Society, 2.30. "The African Rift shortly to appoint the following: A RESEARCH BOTANIST, at commencing salaries of £500 per annum. Application forms and further particulars may be obtained from the Director of Research for the Li en Industry Research Association, 3, Bedford Street, Be fast, to whom the applications for the above Appointments should be sent not later than JANUARY 18, 1920. THE UNIVERSITY OF SHEFFIELD.. DEPARTMENT OF GLASS TECHNOLOGY. Applications are invited for the Post of ASSISTANT LECTURER AND DEMONSTRATOR in the Department of Glass Technology. Candidates should possess an Honours Degree or its equivalent, and should have had good training in methods of Chemical Analysis Special knowledge of Glass Technology not essential. Salary £300 per annum. Applications should be set to the undersigned, from whom further particulars may be obtained, not later than JANUARY 17, 1920. W. M. GIBBONS, Secretary to the Glass Research Delegacy. "The Development If in good condition, Sixpence per copy will be of Mental Tests " by Dr. P. B. Ballard. Royal Institution, 3. "The World of Sound," by Prof. Royal Photographic Society, 7. "The X-Rays approached from a Popular Standpoint," by Dr. G. H. Bodman. Röntgen Society, 8.15. paid for any of the undermentioned numbers of the CHEMIC NEWS which may be forwarded to this office : For Chemical and Bacteriological Research. SPECIALITIES: MARTINDALE'S BURETTE STAND .9/-, 15/ MARTINDALE'S BACTERIOLOGICAL CASE 42/Analytical Price List post free. Telephone-1797 Paddington. W MARTINDALE, 10, New Cavendish St., W. UNTIL recent years evolution has been studied almost exclusively by morphological methods. The most detailed pictures of evolution which we possess, namely, those showing the gradual construction of the modern horse and elephant, have been brought together solely by the inspection of bones; this is unavoidable in the study of extinct forms, since the materials most valuable to the biochemist are not preserved in fossils. The application of experimental methods, as in the study of genetics, for instance, has of course yielded results of the utmost value, but the mode of observation is still chiefly anatomical; the subject of biochemical evolution is still to a large extent untouched. Since organisms which are, anatomically, very simple still exist side by side with others which are very complex, one would think it possible by the study of the composition of both types to investigate the chemical basis of the transition from the one to the other. One may consider here the question of the evolution of proteins. During the past seventy years an immense amount of labour has been expended in attempting to trace the course of the evolution of animals; yet is it possible at the present day to give an account of the steps by which any mammalian protein, for instance the caseinogen of milk, has been produced? Every protein which has been analysed is found to be composed of amino-acids. The amino-acids which have been established as occurring commonly in proteins are seventeen in number (see Note); the composition of these is given in Table I. 1. Glycine.. 2. Alanine.. CH3.CHNH2.COOH CH3 3. Valine CH.CHNH2.COOH CH, CH3\ CH.CH2.CHNH2.COOH CH3 CH3 CH.CHNH2.COOH 4. Leucine 5. Isoleucine CH3 CH2 (NOTE.-Improved analytical methods will no doubt show that the actual number is greater, but this scarcely affects the considerations put forward in this paper. A new amino-acid (3-hydroxyglutamic acid) was discovered in caseinogen quite recently (1); it is omitted from the table because it has not yet been sought in other proteins. Normal leucine is 14. Tryptophane. C6H also omitted because there are as yet very few data as to it distribution. Several others, in addition to the seventeen, have been described (Plimmer, "Chemical Constitution of the Proteins," 3rd Ed., Part I., p. 5). Of these,, some (caseinic acid, caseanic acid, hydroxyar...no succinic acid, hydroxyamino-suberic acid, dihydr- 15. Proline.. cay-diamino-suberic acid, hydroxy-diamino-sebacic acid) are regarde by Plimmer as mixtures, and some others (alamino trioxydodecanic acid, oxytryptophane) are probspond ry products produced in the course of analysis. es of amiac-butyric acid is disputed. The hydroxy-phenylalanine, di-iodotyrosine) are ated to some which appear in the table that. ent point of view, they mely garded. ncy in the yield of pure amino-acids by method, the yield an ounting in many cases to than 50 per cent of the weight of the original nt in itself offe v strong evidence of the existence of undetected amino-acids. The sources of loss, especially in the final isolation and purification of the Fridual amino-acids, are very serious, and it is note that the best yields-80 to 90 per cent-have been d fro those proteins in which a large fraction of molecule is made up of but one or two amino-acids... wheat gliadin with 35 per cent of glutamic acid, silk tour with 60 per cent of glycine+alanine; in such cases the summon of losses incurred in the isolation of a nu her ifferent acids is avoided). namely, (1) it is very limited as regards number, but (2) it is very diverse as regards structure. The total possible amino-acids of complexity lying within the range exhibited by the above ten classes must amount to a very large number. On what basis is this number reduced to seventeen or so? What is the meaning of the curious assortment of ring compounds? Why should two such compounds as, for instance, glutamic acid and tryptophane be chosen? The selection might have been much less, or much more, diverse; as it stands it has a curiously arbitrary appearance. It may, of course, be said that the organism reaches this series of amino-acids, not by any process of selection from a greater number, but through its inability to synthesise any others. This might be so, though it scarcely renders the matter any less remarkable. But in view of the great synthetic capacity of plants, as shown by the structure of alkaloids, for instance, it is difficult to believe that other amino acids could not be synthesised if they were required. Again, it may be said that the existing series of amino-acids has been selected because these, in combination together in varying patterns and numbers, give products which have the properties required of proteins. This is no doubt the case, but it is little more than a paraphase of what is obvious. To attain to any satisfactory knowledge in this direction one requires to know, firstly, what would be the characters of protein" made from an altogether different set of amino-acids, and, secondly, by what process of trial and error the organism succeeded in making the most suitable protein from the most suitable materials. a In seeking for information on the evolution of proteins the higher animals at any rate may be disregarded, since they appear under normal conditions to obtain their amino acids, directly or indirectly, from plants; the limited powers of synthesis which they have been shown to possess are alluded to below. We have so little knowledge of the metabolism of the invertebrates that it is unsafe to assume anything as to their capacities in this respect. Thus, Loeb (2) has shown that the larva of the banana-fly can grow upon a medium containing no nitrogenous substance Other than ammonium tartrate; the experiments did not decide whether this synthesis of protein was carried out by bacteria introduced with the eggs or not. The proteins of higher plants, the wheat-plant, for instance, are known to contain all the amino-acids. The problem of the evolutionary chemistry of proteins, in so far as it is accessible at the prese it day, resolves itself then to this: do the simplest plants (e.g., bacteria, yeast) contain all the amino-acids present in the higher plants? If not, in what plants do the others appear? Such information as is available no this question is given by Plimmer in a table in the latest edition of "The Chemical Constitution of the Proteins " (Part I., p. 127). This shows that various workers have analysed the proteins of five species of bacteria, of yeast, and of a mould (Aspergillus niger); and the table includes analyses of a protozoon (Noctiluca). Table II. is adapted from that given by Plimmer; the composition of caseinogen, a protein peculiar to mammals, has been in cluded for the sake of comparison. The analyses of yeast are those of three different workerst; with regard to four of the amino-acids they are not in agreement. Processes for the isolation of the protein were carried out in the cases of the first four bacteria in the table, and of Neuberg's (9) yeast; Aspergillus niger was extracted with alcohol and ether before analysis; in the remainder f the non(Azotobacter and two yeasts) no separatio protein constituents was attempted, so tha fortunately it is uncertain whether the acids found in them are actually combined as protein. * Analyses of the proteins of other protozoa would be of much interect; mycetozoa, such as Badhamia should provide a sufficient supply of material. Neuberg's (9) paper has been available only in the form of an abstract. The table shows that the five bacteria, yeast, and the mould, taken together. contain all the seventeen aminoacids with the exception of oxyproline, the presence or absence of which was not established, and of serine and cystine, the presence of which was doubtful (in yeast). With regard to oxyproline, "only in a few cases has this compound been isolated from the products of hydrolysis of proteins, since its separation is extremely laborious (Plimmer). It is recorded as present in 8 only of 157 analyses of proteins given by Plimmer. Moreover, proline is present in five of the seven micro-organisms, so that from the present point of view the presence or absence of its hydroxy compound is not of importance. The absence of cystine from the bacterial proteins, which was established by the negative result of a test for sulphur, is noteworthy; this compound is present in numerous proteins of the higher animals and plants.* As the synthetic powers of these organisms are of especial interest it is unfortunate that only two of them were grown upon media of known composition, namely, Aspergillus niger (on MSO4, KH2PO, KCI, FS4 KNO3, cane sugar) and Mycobacterium (on MgSO4, K2HPO4, NaCl, glycerin, ammonium lactate, asparagin). The other bacteria were all grown upon agar or bouilion media, and no doubt some of them could not have dispensed with certain materials, perhaps of the character of vitamines, contained in these complex mixtures. Pringsheim (17) used ordinary "Presshefe," and Meisenheimer (10) yeast which seems not to have been grown on special media; no details as to Neuberg's yeast (9) are accessible. However, one must take these scanty results as all that are at present availabe. They show that the simplest rganisms now existing do hot contain a series of aminoacids any more primitive than that present in the higher organisms, except perhaps as regards the inclusion of kystine. One may suppose that the present apparently stereotyped series of utilisable amino-acids represents the stable outcome of a struggle long ago among simple organisms in which those which made a less suitable choice were beaten, and have passed away leaving no race. We cannot know the biochemistry of the first organisms which appeared upon the earth; the experiments and discarded compounds of that time are lost. The selection of amino acids must have taken place at an immensely remote period, for the earliest records which we have of the forms of life on the earth do not show us organisms which have any appearance of noteworthy difterence in chemical composition from those which exist at the present day. Thus one of the earliest fossils, the brachiopod Lingula of the Cambrian period, is very closely related to a species now living. Structures regarded as fossil Algæ very similar to recent species have been found in still older rocks. The doctrine of natural selection gives the impression that evolution proceeds throughout in a very gradual manner. But at the time wben the aminoacids were first being produced and tested organic evolution must have proceeded very distinctly per saltum as each new compound was synthesised; natural selection would then act slowly and surely upon the organisms which made one or another choice, and thus the present series of amino-acids was delimited. An obstance of the apparently arbitra." nature of the selection is the avoidance of the four-carbon acid, while the 2-, 3-, 5-, and 6-carbon acids are utilised the 3-carbon acid moreover appearing in five forms (alanine, phenyl-alanine, tyrosine, tryptophane, and histidine) and the 6-carbon acid in four (leucine, iso-leucine, normal leucine, and lysine). Some of the amino-acids There is some indirect evidence that cystine is present in the protein of yeast, since this can serve as the sole proteín food of rats (25). Walcott, quoted by Adami, "Medical Contributions to the Study of Evolution," London, 1918 p. 17. The geological history of the bacteria is of course an uncertain matter, depending chiefly upon the inference that various rocks were deposited by bacterial action; the literature on this subject is referred to by Adami ( oc. cit.). TABLE II. (Blank spaces indicate that the presence or absence of the amino-acid was not determined). may have been chosen because of their suitability, not only for the formation of proteins, but for the production of other compounds as well. Thus arginine and histidine may serve as sources of purines (12); proline is closely related to a group present in chlorophyll and hæmoglobin; and tyrosine to adrenalin and perhaps some pigments. One does not of course suggest that the earliest organisms provided for the future formation of substances such as chlorophyll and adrenalin; but the various chemical possibilities of these amino-acids may be utilised by the simplest plants in their metabolism in ways which we do not know of. Pringsheim (17) has considered this point in the case of yeast. There is obviously much to be learned as to the experimental methods by which organisms arrive at the production of suitable substances, for any given new compound cannot be brought into existence gradually. The final, or rather the present, product is in many cases a highly successful one (e.g., the superiority of adrenalin to many allied compounds (13); the great potency of snake venom), but the preceding stages are effaced by natural selection. Very little seems to be known also of the method of synthesis of the amino-acids in plants; possibly the plant makes from dextrose those members of the series which the mammal can convert into dextrose. It has long been taught that animals are dependent ultimately upon plants for their supply of protein. Knoop '15 and Embden and Schmitz (17) and their fellow workers (18, 19) showed however, in some experiments which attracted a great deal of attention at the time (1910), that mammals have some power of synthesising amino-acids. But surely these experiments, striking as they are, reveal chiefly the feebleness of this synthetic power in animals; they seem rather to emphasise how completely parasitic upon the plant the animal has become. It was shown that the mammal, when supplied with certain a-keto-acids, could convert them into the corresponding a-amino-acids whether these were of natural occurrence (alanin, phenyl-alanın, tyrosin, a-amino-caproic acid) or not (a-amino-butyric acid, y-phenyl-a-aminobutyric acid). But this insertion of an -NH2 group is no great synthetic achievement. Firstly, as Knoop points out, this change in keto acids may occur in vitro simply in the presence of ammonium carbonate. Secondly, there was admittedly nothing in the experiments to show that the mammal could itself provide the essential molecule to which the NH2 group was to be attached, except the very simple (that of pyruvic or lactic acid) required for the producion of alani It is known further that mammals can produce the simplest amino-acid glycin; but whether by a synthetic process or otherwise is not clear (20). Tyrosine can be formed in the liver under experimental conditions from phenyl-alanine (14), and hence appears not to be an essential constituent of diet (15). Whether phenyl-alanine can be synthesised has not yet been shown. This appears to be all the evidence + + + + + 1 which we have for the synthesis of amino-acids by mammals. On the other hand, tryptophan (21), lysine (22), arginine and histidine (12), and apparently cystine (23) cannot be synthesised by the higher animals. Van Slyke (24) has laid stress on the fact that we have no evidence either for or against their power of synthesising any one of the remaining amino-acids, at least ten in number, other than those mentioned above. But it is obvious, from their inability to live upon the simple materials which suffice for plants, that their synthetic powers are at least immensely inferior. The work of Abderhalden and Rona (4) and of Tamura (5), alluded to in Table II., provides an i lustration of this familiar fact. In their experiments, Aspergillus niger grew equally well, and formed the same amino-acids, whether its nitrogen were supplied in the form of potassium nitrate, or of glycin, or of glutamic acid, and the protein of mycobacterium showed the same composition whether the medium were peptone-bouillon, or one containing no nitrogenous compounds but ammonium lactate and asparagin. No higher animal can do anything of this sort. The fact that no amino-acid which enters into the composition of proteins has been shown to be peculiar to animals has perhaps hardly received sufficient attention; it alone would demonstrate that their synthetic activities in this field, whatever they may be, are nowhere more extensive than those of plants. Though the matter is a very familiar one, it is perhaps worth while to consider here for a moment the chemical powers of yeast. In the time taken by a yeast cell to produce another by budding* when growing on a medium such as Pasteur's, containing no nitrogen but that of ammonium tartrate, it must synthesise each one of the amino-acids given for yeast in Table II., and combine them as a series of polypeptides until its proteins are produced, and all the while carry on many other chemical operations. Even when one takes into account the small size of molecules it is wonderful that so many reactions can be kept apart within the compass of a yeast cell. One may compare with the obvious growth of yeast the amount of experimental procedure required to bring to light the partial synthesis of a single amino-acid in a mammal and realise what has been lost in the course of evolution. Specialisation is largely a process of loss of capacities; some zoological teaching has perhaps represented it too largely as a progressive development.† Since the higher animals cannot synthesise some of the amino-acids which are essential to their life the plant world has so to speak a power of blockade over them. If the pre dominant vegetation of the world entered upon a phase of evolution in which it provided but an inadequate supply of one of these amino-acids, animals would have to adapt themselves to this, though man could of course circumvent any such change by cultivation. It is conceivable that this has happened in the past; thus during the close of the Secondary Period an astonishingly diverse and abundant fauna of reptiles of great size passed out of existence, and it is difficult to believe that the competition of other animals was sufficiently formid. able to bring this about. 7. TAMURA. Ibid., 1914, xc., 286. 8. OMELIANSKY U. SIEBER. Ibid., 1913, lxxxviii, 445. 9. NEUBERG. Woch. f. Brauerei, xxxii., 317; Chem. Zentr., 1916, i., 162. 10. MEISENHEIMER. Zeitschr. f. Physiol. Chem., 1919. civ., 229. II. PRINGSHEIM. Woch. f. Brauerei, xxx., 399; Chem. Zentr., 1913, ii., 1310. 12. ACKROYD and HOPKINS. Biochem. Journ., 1916, x., 551. 13. DAKIN. Proc. Roy. Soc., B, 1905, lxxvi., 498. 14. EMBDEN U. BALDES. Biochem. Zeitschr., 1913, lv., 301. Biochem Journ., 1916, x., 382. 15. TOTANI. 16. KNOOP. 486. Zeitschr. f. Physiol. Chem., 1910, lxvii., 17. EMBDEN U. SCHMITZ. Biochem. Zeitschr., 1910, xxix., 423, and 1912, xxxviii., 393. 18. FELLNER. Ibid., 1912, xxxviii., 414. 19. KONDO. Ibid., 1912., xxxviii., 407. 20. See references given by Lusk. 21. 22. 23 24 25. "The Science of Sample 2 was not the clear white deposit obtained before, but showed contamination with the black oxide above mentioned. Samdle 3, obtained from a fresh solution of the double salt, was white. It was obtained with a voltage of 4 and a current density of 1.63 amp. The similarity of the behaviour of the white deposit, when heated, to the behaviour of uranium tetrafluoride when it was heated, suggested that the deposit might be a Aluoride of uranium. This was proven to be correct as the following analysis shows:-Tests for fluorine were made by placing one of the electrodes in a large platinum dish, adding concentrated sulphuric acid, and covering the dish with a glass plate coated with paraffin. The design drawn in the paraffin was not etched in any case though From the Journal of Physical Chemistry, xxxiii., No. 8, |