ELEMENTAR Y COMPOSITION OF OXYH^MOGLOBIN. 201 



Varrentrapp), though the results which he obtained differed in a remarkable 

 manner from all those of previous observers. It is clear that whilst very great 

 value must be attached to the determination of the iron and sulphur contained in 

 haemoglobin, made by Zinoffsky, his conclusions as to the percentage of carbon 

 and hydrogen must be rejected, as being based upon an insufficient number 

 of analyses, and as being in all probability incorrect. This opinion is supported 

 by the remarkable discrepancy between his results and those of other observers 

 a discrepancy which cannot be accounted for by differences in purity of the 

 bodies analysed. 



While it is almost inconceivable, and against the weight of evidence, that 

 haemoglobin derived from animals of the same species should not have a 

 constant composition, the differences in centesimal composition which certainly 

 do exist between the haemoglobin of certain animals and that of others 

 cannot surprise us when we reflect that haemoglobin does exhibit marked 

 physical differences in different animals that it exhibits variations in 

 crystalline form, in the amount of water of crystallisation, and in solubility. 



The study of the general results of the ultimate analyses of oxy- 

 haemoglobin made of recent years forces us assuredly to the conclusion 

 that new and still more precise investigations are needed before we can 

 lay claim even to so limited a knowledge as that of its precise centesimal 

 composition. Nevertheless, it would be wrong to leave the study of 

 the more recent researches without drawing attention to certain of the 

 numerical results obtained, which are more deserving of confidence 

 than others. 



The most characteristic and the most important of the elements 

 which enter into the composition of haemoglobin is its iron. Iron is 

 the typical element in a molecular group which exists and possesses 

 identical chemical and physical properties in all the varieties of 

 haemoglobin with which we are acquainted. Besides furnishing us 

 with data by which the molecular weight of haemoglobin may be 

 calculated, the amount of iron appears to bear a definite relation to 

 the quantity of the dissociable oxygen and carbonic oxide which 

 haemoglobin combines with. For these reasons, an extremely accurate 

 determination of the iron in haemoglobin, carried out with all the 

 precision which the present state of science permits of, has been a great 

 desideratum. Such determinations have been carried out by Zinoffsky, 

 Jaquet, and Hiifner (see p. 199). 



These observers have determined the proportion of iron in the 

 oxyhaemoglobin of the dog, the horse, the ox, the pig, and the hen. 

 They have shown : First, that the amount of iron in the blood-colouring 

 matter of these animals is decidedly smaller than had been assumed 

 on the basis of the older analyses. Secondly, that in the animals 

 mentioned the percentage of iron in the haemoglobin is identical, so 

 that we may conclude that in these very different animals, in spite of 



