OUTLOOK. 691 



hemolysis takes place on the addition of cobra poison. The addition of 

 a little serum, or of lecithin, now suffices to cause hemolysis. It is natural 

 to designate lecithin as the amboceptor which enables the poison of the 

 cobra to attack the erythrocytes. It is, furthermore, interesting to find 

 that cholesterol can prevent this action of the lecithin. We mention 

 these interesting discoveries here because they perhaps explain why the 

 two compounds, cholesterol and lecithin, are found in every cell. 



There is no doubt that red blood-corpuscles are constantly being de- 

 stroyed in our organisms. Hemolysis undoubtedly takes place. It may 

 be brought about by changes in the osmotic pressure, but it is also possible 

 that the normal destruction of the red corpuscles results from a process 

 similar to that just described. 



We may add that the formation of precipitins may also be explained on 

 the basis of Ehrlich's side-chain theory, and many other discoveries find 

 their proper place in complicated processes by means of the same theory. 



We have now reached the end. We are aware that we have just placed 

 considerable stress upon a mere hypothesis, and realize the danger that may 

 result from such a generalization. On the other hand, we are able, in each 

 particular case, to decide whether we are justified in comparing a given 

 process with those which have been just described. It is clear that the 

 final goal of our investigation in the field of immunization is never to be 

 attained by the mere advancement of any special theory. We find our- 

 selves temporarily in a region which is not accessible to chemical or 

 physical investigation, for both require as a starting-point the employment 

 of chemically pure substances. As long as we are unable to prepare any 

 one of these complicated products in a pure state, and establish its 

 chemical constitution, we must not expect to obtain an exact insight into 

 all the complicated processes upon which the actions of the toxines and 

 related substances are based. 



