224 



NATURE 



[January 3, 1901 



national income, are in store for us, we shall have, because 

 of this condition of things, to face a constantly increased 

 expenditure upon our fleet. 



These considerations are only typical of others which 

 are well worth considering at the present juncture by 

 men possessing the scientific spirit. What is the best 

 way of utilising the combined forces of the Empire, in 

 times of peace, under the present conditions ? It is clear 

 that no merely sentimental bonds will be sufficient. We 

 may add that peaceful conflicts between industrial peoples 

 are not alone in question. 



With regard to preparation for war, history has 

 already taught us much. Of two competitors, if one 

 be fully armed both for offence and defence, and the 

 other is not, there is no doubt as to what will happen. 

 That nation will be the best off which utilises the greatest 

 number of its citizens both for war and peace. A large 

 standing army in times of peace is a clear indication 

 that the scientific spirit has not been sufficiently applied 

 to the problem, and it is to be hoped that now the future 

 of the Nation is being discussed, the attempts to put our 

 house in order will be made on scientific lines. 



Editor. 



RECENT ADVANCES IN THE CHEMISTRY 

 OF THE PROTEIDS. 



Chemie der Eiweisskbrper. Von Dr. Otto Cohnheim. 

 Pp. X + 315. (Braunschweig : F. Vieweg und Sohn, 

 1900.) 



SINCE the publication of Drechsel's article on proteids 

 in Ladenburg's Encyclopaedia, no complete account 

 of the chemistry of the proteids has appeared. The 

 accounts given in the best known text-books of physio- 

 logical chemistry are necessarily brief and incomplete. 

 Dr. Cohnheim's book is therefore a very welcome addi- 

 tion to the literature of physiological chemistry, giving, 

 as it does, a detailed account of the present state of 

 knowledge with regard to the proteids. 



The book is divided into a general and a special part. 

 The first deals with the physical and chemical properties 

 of the proteids, then with the products of their decom- 

 position, and finally discusses their structure and classifi- 

 cation. In the second part, the characteristics of the 

 different forms of proteids are considered in detail. 



In reviewing the book as a whole, it is impossible to do 

 more than emphasise those features in which it shows a 

 distinct advance as compared with its predecessors. 



The chief characteristics which distinguish the pro- 

 teids as a sharply limited class of organic compounds are 

 the following. They contain the elements carbon, 

 hydrogen, oxygen, nitrogen and, as a rule, sulphur in 

 fairly constant proportions, and although their constitu- 

 tion is as yet unknown, the similarity in their chemical 

 behaviour is so great that they may all be regarded as 

 having a common chemical structure. Provisionally they 

 may be divided into three groups, the native simple pro- 

 teids, the compound proteids — in which a simple proteid 

 is united to some other organic body — and the earlier de- 

 composition products which still retain, in large measure, 

 the chemical properties of the proteids from which they 

 NO. 1627, VOL. 63] 



have been derived. The compound proteids may con- 

 tain, in addition to the elements already mentioned, 

 phosphorus and iron. 



Their properties may be divided into physical and 

 chemical. Taking the former first, the author selects, as 

 their most characteristic property, the tendency of all 

 native proteids to pass readily out of solution in the form 

 of a more or less permanently insoluble precipitate or 

 coagulum. 



Means otherwise chemically indifferent, such as 

 mechanical agitation of their solutions, contact with 

 porous substances, or evaporation of part of the water 

 of solution, result in the separation of a flocculent pre- 

 cipitate, which, on microscopic examination, is found to 

 consist of minute particles tending to cohere so as to 

 form membranes or threads of coagulated proteid. It 

 is this property of proteids which explains their indiffusi- 

 bility and the difficulty with which they undergo crystal- 

 lisation. 



Chief amongst the physical agents which produce this 

 change is heat. To the subject of coagulation by heat a 

 special chapter is therefore devoted. In the presence of 

 a fixed quantity of neutral salt of the metals of the 

 alkalies, and a very faint acid reaction, the temperature of 

 coagulation is fairly constant for each native proteid, and 

 has proved of considerable value in their separation and 

 classification. A variation in the quantity or nature of 

 the salt used alters the temperature of coagulation of any 

 given proteid. Further, the proteid that separates out 

 from a faintly acid solution carries with it some of the 

 acid, so that the solution after coagulation is found to be less 

 acid than before, or may even be neutral. The latter fact 

 renders the coagulation of proteids by heat specially liable 

 to fallacy as a method for their separation. The part played 

 by the neutral salt in heat coagulation is still doubtful. 

 Most observers have found that proteids, in solutions freed 

 as far as possible from salts by dialysis, do not coagulate 

 on heating ; but the addition of a small quantity of 

 neutral salt to the previously heated solution results in the 

 separation of a coagulum. Cohnheim, therefore, regards 

 coagulation by heat as invariably associated with the 

 formation of an acid albumin insoluble in salt solution ; 

 but soluble in the least excess of the acid used. The evi- 

 dence, however, on the influence exerted by neutral salts 

 on the temperature of coagulation is conflicting. There 

 is evidence that, in some cases, a proteid solution, freed as «i 

 far as possible from salts by means of dialysis, coagulates S 

 at a lower temperature than when a small quantity of 

 neutral salt is present. By means of dialysis alone it has 

 not, as yet, been found possible to obtain a native proteid 

 free from ash, so that the influence of heat upon a native 

 proteid solution free from mineral matter has not yet been 

 studied. 



The next section of the book deals with the methods 

 used for salting out proteids, and contains a complete 

 account of the relative value of various salts as precipi- 

 tants. Of all salts of the metals of the alkalies and 

 alkaline earths, ammonium sulphate has the greatest 

 precipitating power. Saturation with it precipitates all 

 the native proteids from solution, and, with the exception 

 of peptone, all the products of peptic or tryptic digestion 

 still retaining proteid characters. Its precipitating power 

 is increased by the addition of dilute acids, and, in the 



