226 



NA TURE 



[January 3, 1901 



either directly or by means of an atom of carbon or 

 nitrogen. The oxygen in the CONHg groups may be 

 substituted for sulphur without interference with the re- 

 action. As all proteids give this reaction, the proteid 

 molecule must contain at least one organic group corre- 

 sponding to one of the three forms described by Schiff. 



The simplest forms of proteid, the protamines, and 

 their digestive products the protones, give the biuret re- 

 action, but none of the other colour reactions of the 

 proteids. 



Kossel gives (CgoHgyNiyOg)™ as the formula of clupein, 

 one of the most thoroughly examined protamines. On 

 further hydrolytic decomposition, the protones yield the 

 hexone bases, arginin, CeHi4N402 (guanidin-a-amido- 

 propionic acid), and histidin, CoHgNgOg, a base of un- 

 known constitution. The hexone bases appear to be the 

 only primary products of decomposition. Their relative 

 proportion varies considerably, according to the particular 

 protamine examined. None of these hexone bases give 

 the biuret reaction, nor does any other one of the pro- 

 ducts of decomposition of the proteids of known constitu- 

 tion. The biuret reaction is therefore in general use as a 

 criterion, distinguishing the proteid bodies in the widest 

 sense from their simpler products of decomposition. 



The protamines are chemically and, as the work of 

 Miescher and others has shown, probably genetically the 

 precursors of the more complex forms of proteid. The 

 basic organic groups in proteid which give the biuret re- 

 action are also the most resistant to the action of diges- 

 tive enzymes, and make up the greater part of Kiihne's 

 so-called anti-group. Starting from these facts, Kossel 

 has suggested that the nucleus of the proteid molecule 

 has a structure resembling that of protamine. To this 

 nucleus other organic groups become added, so as to 

 form proteid bodies of more complex structure, and he 

 has suggested that upon these facts might be founded a 

 chemical classification of the different proteids. The 

 steps of the synthesis of proteids within the organisms of 

 plants and animals are still, however, too vaguely known 

 to admit of such a classification. Further, Kossel's con- 

 jecture has not proved to agree completely with the facts, 

 proteids being known which give a well-marked biuret 

 reaction, although, upon hydrolytic decomposition, they 

 yield a relatively small quantity of the hexone bases. One 

 may therefore conclude that proteid bodies giving the 

 biuret reaction do not always contain a protamine nucleus 

 in the sense originally suggested by Kossel ; but the evi- 

 dence that a group of basic character giving the biuret 

 reaction forms the nucleus of the proteid molecule is 

 fairly conclusive. The biuret group may belong to any 

 of the types defined by Schiff, and there is evidence that 

 several biuret groups are present in the more complex 

 proteids. One of these groups contains a relatively large 

 percentage of sulphur. 



The majority of the other colour reactions of the pro- 

 teids are dependent on the presence of an aromatic or 

 of a carbohydrate radicle. Millon's reaction is given 

 only by bodies which contain a benzene group in which 

 one atom of hydrogen has been substituted for hydroxyl. 

 The xanthoproteic reaction indicates the presence of 

 a benzene group. 



The colour reactions resulting from the presence of a 

 carbohydrate radicle may be grouped together as furfurol 

 NO. 1627, VOL. 63] 



reactions. On heating with mineral acids many of the 

 proteids yield furfurol, which may be detected by the 

 colour reactions which it gives with a-naphthol and 

 thymol. In those proteids which contain both an aromatic 

 and a carbohydrate group, the addition of thymol or 

 a-naphthol is unnecessary, a colour reaction being ob- 

 tained by the action of the furfurol on an aromatic radicle 

 split off from the proteid itself. The chief reactions which 

 indicate the presence of a carbohydrate as well as an 

 aromatic group'are those of Liebermannand Adamkiewicz. 

 There are a number of other colour reactions which, 

 as yet, have not been so carefully studied as those already 

 mentioned. Of these the most important are Petri's 

 diazo-reaction, which is also given by the hexoses and 

 is, therefore, probably dependent upon a carbohydrate 

 group, Wiirster's quinone reaction, which appears to 

 depend on the presence of the tyrosine group in proteid, j 

 and Reichl's reaction with benzaldehyde, which is also a| 

 given by indol and scatol. Dr. Cohnheim has omitted 

 the discussion of the latter reactions, possibly because 

 their significance has not been sufficiently determined. 



Within the limits of a review it would be impossible to 

 discuss the next section of the book, which deals with 

 the simpler products of the decomposition of proteids 

 resulting from the action of various hydrolytic agents, 

 concluding with a very interesting account of the pro- ; 

 cesses of decomposition in the metabolism of plants and 

 animals. 



After completing the study of the products of decom- 

 position. Dr. Cohnheim gives a suggestive summary of 

 the views held with regard to the mode of union of the 

 elements present in the proteid molecule. It is note- 

 worthy that in no part of the book is an account given of 

 the various attempts to synthesise proteids. 



At the outset of the following chapter, on the classifi- 

 cation of proteids, the author shows a certain hesitation 

 in adopting the usual method of classification, but ulti- 

 mately decides that at present it is impossible to give a 

 satisfactory classification based upon differences of 

 chemical structure. He therefore practically adopts 

 Hammarsten's latest classification, which, with some 

 modifications, is essentially the Same as that proposed by 

 Hoppe-Seyler and Drechsel about fifteen years ago. 



Limits of space will not permit one to give more than ^ 

 a brief reference to the remainder of the book. In the ^^ 

 order of treatment of the subject. Dr. Cohnheim ha& 

 adopted a significant departure from the order of classifi- 

 cation. 



An analogy is frequently drawn between the proteids 

 and the carbohydrates in the sense that the native pro- 

 teids are considered to bear to the primary products of 

 their hydrolytic decomposition, namely, the proteoses- 

 and peptones, a relation similar to that which the more 

 complex polysaccharides bear to the dextrins. 



Under the influence of this analogy. Dr. Cohnheim 

 deals with the chemistry of the proteoses and peptones 

 before commencing his detailed account of the individual 

 forms of proteid. One almost regrets that the author 

 had not departed still farther from the usual order of 

 treatment. Following Kossel's suggestion, he might first 

 of all have dealt with the hexone bases and their anhy- 

 drides, the protones and protamines. Kossel originally 

 proposed the name hexone-bases to mark the analogy 



