Ill 



of experience of a few toxins, especially that of diph- 

 theria, we had reached a point where we could extend 

 this principle of measurement to others. So long as 

 these measurements could only be practised on living 

 animals, the number had in the nature of things to be 

 strictly limited. It was therefore a great step forward 

 when Ehrlich introduced experiments with test tubes, 

 for the measurement of toxins and antitoxins and dis- 

 covered bodies, whose reaction was recognizable in vitro. 

 We have just such a body in the tetanolysin 1 ), which by 

 simple colorimetric methods can be measured with great 

 exactitude in vitro. It has this great advantage, that it 

 is neutralised by its antitoxin in an apparently similar 

 manner to the diphtheria toxin, hitherto the most tho- 

 roughly studied of the toxins. 



The tetanolysin must therefore be looked upon as 

 very well suited to quantitative determinations and there- 

 fore to physico-chemical studies, as the manner of ex- 

 perimenting in vitro allows variations in the conditions 

 of experiment, to a much greater extent than is the case 

 with living animals. If we take, for instance, the velocity 

 of reaction between tetanolysin and red blood corpuscules 

 or between tetanolysin and antitetanolysin, or the influ- 

 ence of temperature, this could only be investigated 

 with great difficulty if at all in animal experimentation.. 



The first thing to be done was to procure a large 

 amount of data and of such a kind, that it could be 

 easily accessible for the theoretical calculations used in 

 physical chemistry. A cooperation between two persons 

 could hardly be dispensed with. One was needed to see 

 that the experiments w r ere made systematically from a 

 physico-chemical stand-point; another had to be familiar 



') Th. Madsen: Ueber Tetanolysin, Zeitsehr. f. Hygiene etc. XXXII. 1899. 



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