IV 



Obituary Notices of Fellows deceased. 



possesses an atom group, by which it is linked to the side-chains of the 

 cell protoplasm, and a toxic group which produces the characteristic lesion 

 or symptoms ; and, by an extensive series of researches, he studied the 

 changes occurring in a toxin in the process of deterioration. He early 

 formed the view, and demonstrated by test-tube experiments, that antitoxin 

 combines directly with and neutraUses toxin — not by destroying its toxicity, 

 but by satisfying its combining affinity, so that it no longer unites with the 

 cell protoplasm ; and it may be noted that the dissociation of toxin from 

 antitoxin has since that time been demonstrated. He further supposed that 

 toxin molecules resembled in constitution, or masqueraded as, foodstuffs, and 

 were fixed to the cell protoplasm by its side-chains. Owing to their being 

 lost for the purposes of the cell, they are cast off, still in combination with 

 the toxin ; the side-chains are reproduced, and, when the process is continued, 

 they are reproduced in excess, and set free in the blood. These free side- 

 chains or receptors are then in a position to act as antitoxin, combining with 

 any toxin present, and preventing its union with the cells. Such, in brief, 

 is Ehrlich's side-chain theory as evolved in the case of antitoxins ; it was 

 afterwards elaborated to explain more complicated anti-substances, agglu- 

 tinins, lysins, etc. 



We have seen how, in his earlier researches, Ehrlich demonstrated the 

 selective affinity which definite chemical compounds have for the constituents 

 of cells in the li^dng or dead condition, whilst in antitoxic action there is an 

 affinity which has within certain limits a specific character. This specific 

 character he supposed to rest on the complicated structure or configuration of 

 liAdng matter, and the essential point in his side-chain theory is that anti- 

 substances pre-exist in the cells, and become free as the result of the 

 stimulus to over-production. The number of anti-substances is apparently 

 without limit, and it may be objected that their pre-existence is incon- 

 ceivable ; but, in view of the established facts, the same criticism applies 

 to any theory that can be put forward. The determination of the value 

 of Ehrlich's side-chain theory will, however, be attained by future experi- 

 mental work, not by discussion. The natural sequence to the work on 

 antitoxin action was an extension of the enquiry to other anti-substances 

 more complicated in their structure and mode of action, and the outcome at 

 a later date was a long series of researches dealing especially with the 

 lysins. These are of an intricate nature, but are essentially dominated by 

 his previous views, and are characterised by imagination and ingenuity 

 of plan. 



Apart, however, from Ehrlich's theoretical contributions to this biological 

 problem, his work on antitoxin led to practical results of the highest value. 

 One of the chief features of his genius was the combination of imaginative 

 outlook with the power of detailed working out ; rarely has this combination 

 been so remarkable as in his case. Standardisation of antitoxin was 

 essential to successful therapeutics, and Ehrlich, in his capacity as Director 

 of the Serum Institute, attacked the problem with his usual thoroughness. 



