Paul Ehrlich. 



V 



He investigated in great detail the phenomenon of antitoxin production in 

 the body, the nature of its neutralising action, and, what was a problem of 

 great complexity, the changes which occur spontaneously in toxins. The 

 last, in fact, were a bar to standardisation of toxin for practical purposes, but 

 Ehrlich solved the problem by introducing a standard antitoxin, which, by 

 means devised by him, could be kept practically unchanged. His method of 

 standardisation has remained the one in general use down to the present day, 

 and by means of it the method of antitoxin treatment has been stabilised 

 and the value of the results enhanced. 



Ehrlich's official work at Frankfurt, from 1901 onwards, included investiga- 

 tions into the nature of tumour growth, and these were carried out on a very 

 extensive scale. Though no therapeutic results were reached, there followed! 

 many important additions to knowledge on the biological side, with regard tO' 

 the conditions of growth and virulence of malignant tumours, the production 

 of immunity, modifications of structure in relation to virulence, etc. ; in fact, 

 for a time, the work from Ehrlich's laboratory may be said to have largely 

 dominated this field of research. The principles of immunity to bacterial 

 disease were naturally brought to bear on the question, and methods were 

 devised by which an analogous active immunity could be produced against a 

 tumour otherwise invasive — the tumour, needless to say, being derived from 

 another animal. The natural immunity possessed by an animal against a 

 tumour from a different species is in a different category ; it is due, not to 

 destructive powers on the part of the animal, but to failure of the cancer cell 

 to draw nourishment from the fluids of the host. The special feature of the 

 cancer cell, according to Ehrlich, is an excessive avidity for nourishment, yet 

 the cell fails to grow in any but the fluids of the species of animal from 

 which it has come. Here again, just as in the case of anti-substances to 

 proteins introduced parenterally, species-differences in molecular structure 

 are brought out in a striking way. 



To the failure of growth of the cancer cells in the conditions last mentioned, 

 Ehrlich applied the term athrepsy, and described it as due to a want of 

 correspondence between the cell receptors and the available food molecules. 

 He analysed this athrepic immunity, and found that the same principles 

 held in various bacterial and protozoal infections, as well as in chemo- 

 therapy, there being in all of them examples of the want of fixation as 

 a preliminary to the necessary action. 



It will be gathered from what has been said above, that Ehrlich drew a 

 close parallel between the taking up of food molecules by a cell and the 

 fixation to the cell of certain substances which act as poisons — both depend 

 upon the presence of suitable side-chains or receptors in the cell protoplasm. 

 Accordingly, the failure of a poison to act as such is often due to non- 

 combination with the cell. 



The application by Ehrlich of the principles just explained led to 

 remarkable results. Using, in the first instance, trypanosome infections 

 as the test, he found that a large number of substances had a marked 



