THE PRECIPITINS AND THEIR ANTIBODIES 297 



lytic substances, such as tetanolysin, are bound to the sub- 

 stance acted upon, so that a given quantity of lysin can 

 lake only a given equivalent quantity of erythrocytes (cf. 

 pp. 104, in). Even for the agglutinins such an equivalence 

 has been observed. It is a general feature of the theory of 

 Ehrlich that he assumes that the action of poisons depends 

 upon a binding, or as he often says an "anchoring," of the 

 poison to the substrate upon which it acts. In this regard 

 Ehrlich goes however a little too far, since he, for instance, 

 supposes that all the immune-body absorbed by an ery- 

 throcyte is " anchored " to it. 



Furthermore, we have found that on neutralising a 

 poison or an analogous substance with its antibody, a real 

 binding takes place according to stoichiometrical propor- 

 tions. It may here be observed that in some cases and 

 these are perhaps rather common (cf. p. 267), as for in- 

 stance in the coagulation of casein the reacting substance 

 is really not a single one but two, rennet and calcium ions ; 

 the antibody (e.g. that from normal horse-serum) binds 

 only the one component of the reacting mass (here the 

 calcium ions), probably leaving the rennet intact. In simi- 

 lar cases it is very easily possible that the one component 

 that is not bound by the antibody acts as a catalysor. 

 This seems very probable for rennet, as the time necessary 

 for coagulation is within very wide limits inversely pro- 

 portional to its quantity. 



Nevertheless, on the whole, we obtain from a closer 

 study of these phenomena the opinion that the catalytic 

 action does not play the chief r61e which has been often 

 assigned to it by different authors. Ehrlich has on re- 

 peated occasions rightly laid stress upon the necessity of an 



