B.— CHEMISTRY. 57 



of separating aspartic and glutamic acids by their calcium salts, Dakin 

 discovered hydroxyglutamic acid, an entirely unsuspected unit of protein. 

 A knowledge of the structure of amino-acids may throw light on how 

 other nitrogenous constituents arise, particularly in plants. As an 

 example, the most recently discovered amino-acid may be quoted. The 

 American bacteriologist Mueller found in casein and other proteins a new 

 constituent containing sulphur, quite different from the well-known 

 cystine. Dr. Coyne and I have recently established its constitution by 

 synthesis. It turns out to be Y'^^^thylthiol-a-amino-n-butyric acid, 

 CH3.S.CHo.CH(NH2)COOH, and we named it methionine. The methyl- 

 thiol grouping at once indicates that it is the source of methylmercaptan, 

 the occurrence of which in putrefaction was known, although not hitherto 

 inteUigible. Methionine is evidently also the parent substance of cheiroUn 

 occurring in the seeds of the wallflower and of other Cruciferae. Schneider 

 had long ago established for this substance the remarkable constitution 

 CH3.SO2.CH2.CH2.CH0.N.CS. We now see at once that cheirolin is the 

 thiocarbimide of oxidised and decarboxylated methionine. Similarly 

 Perkin and Robinson connected the chemistry of harmine and harmahne 

 with tryptophane when they showed that the mysterious base C12H10N2, 

 which Hopkins and Cole obtained by oxidising tryptophane CiiHi20.^N2 

 with ferric chloride, is identical with harman 



This observation not only settled the constitution of the alkaloids in 

 question, but also explained the fitful yield of the oxidation product of 

 tryptophane, which, after decarboxylation, had condensed with acetalde- 

 hyde. Soon afterwards Spath showed that harman itself occurs in nature, 

 as the alkaloid aribine, which had been given the erroneous formula 

 C23H20N4. It is becoming increasingly evident that many alkaloids arise 

 by condensation of amino-acid residues. Mezcaline and other alkaloids 

 of Cactaceae are closely connected with phenylalanine and tyrosine, as 

 Spath has shown, and the mode of origin of isoquinoline alkaloids from 

 aromatic amino-acids has also become clear. Harmine, harmaline, 

 physostigmine, and rutaecarpine are all derived from tryptophane, and 

 it looks as if the same is true of other alkaloids whose constitution, like 

 that of strychnine and of brucine, remains obscure. 



The isolation of some natural substances, of great physiological interest, 

 is beset with difficulties because they are present in minute amount and 

 have not the convenient solubility relations whichj facilitate the separa- 

 tion of the alkaloids. This applies to the hormones present in animal 

 tissues. Here the American slaughter-houses provide valuable faciUties, 

 and it is significant that adrenaline, thyroxine, and insuUn were first 

 crystallised in America, although the constitution of the two former 

 hormones was later established in Europe, where also their synthesis was 

 effected, that of thyroxine only a few years ago, through the brilhant 

 work of Harington. The difficulties of isolating vitamins is still more 

 formidable ; in the case of the antineuritic vitamin B, which is almost 



