Paul Ehrlich. 



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regarding the sources of leucocytes and their behaviour in reactive processes. 

 Further, he published numerous papers on the anaemias, leucaemias, etc., and 

 his observations still constitute the foundation of htematology. We owe to 

 him also many important methods, e.g., those for demonstrating glycogen in 

 cells, for estimating the reaction of the blood, the diazo reaction, etc. And 

 we owe to him also the demonstration of the acid-fast character of the 

 tubercle bacillus and the method of demonstrating it, which is still in 

 general use. 



We have already indicated that Ehrlich's researches on stains had as their 

 object not so much the obtaining of new histological methods, though these 

 were supplied, as the throwing of light on the larger question of combining 

 affinity, and it was accordingly natural that he should extend his principles 

 to the living organism. The outcome of research in this domain was twofold, 

 viz., the discovery of the intra-mtam method of staining, and his work on the 

 oxygen requirements of the organism. By the injection of methylene blue 

 into the circulation, or by placing a small living organism in the dye, he was 

 able to demonstrate the processes of certain nerve-celia down to their finest 

 endings. It is unnecessary to refer to later developments of this method, or 

 to emphasise the importance which it has had in biological study. 



His monograph, 'Das Sauerstoffbediirfnis des Organismus,' published in 1885, 

 contains an account of experiments on the relative affinity of the tissues for 

 oxygen. In these he employed two dyes, viz., alizarin blue and indophenol, 

 both of which are reducible to leuco-compounds, the latter being the more 

 readily reduced. On introducing one of these dyes, in a colloidal state, into 

 the circulation of an animal, and killing the animal some time afterwaids, he 

 found that some organs were coloured blue, whilst others had reduced the 

 dye and contained the leuco-product. Further, some organs which ordinarily 

 did not reduce the dye did so when a state of asphyxia was established. By 

 these methods he was able to deduce the relative reducing powers of different 

 tissues for oxygen, and he explained the results on the supposition that there 

 exist side- chains in the cell protoplasm, whose function is the fixation of 

 oxygen for cellular needs, and that the affinity of these varies in different 

 organs. In this work the germ of his side-chain theory is found. 



The next period of Ehrlich's work was occupied chiefly by the study of the 

 action of toxin and antitoxin. In 1891 he published papers on ricin and 

 abrin, in which he showed that antitoxins to these vegetable toxalbumens 

 could be produced by feeding certain animals with sublethal doses. 

 Accordingly, antitoxin production was not peculiar to the case of bacterial 

 toxins, nor was it essential that the poison should be introduced pareuterally. 

 He showed also that immunity to these poisons could be transmitted from 

 the mother to the offspring, and that this was due to the direct passage of 

 antitoxin from the blood of the former, chiefly through the milk ; in other 

 words, the immunity is of the passive order. From a study of toxins and 

 their action, Ehrlich formed the view that a toxin has essentially a dual 

 constitution, and that there are two essential factors in its action. It 



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