I lay great stress upon these statements, as I should like to be as careful as possible in the admission of anything like a “proof” of vitalism. It was want of scientific criticism and rigid logic that discredited the old vitalism; we must render our work as difficult as possible to ourselves, we must hold the so-called “machine theory” of life as long as possible, we must hold it until we are really forced to give it up. In a more general form we now can sum up our discussion by saying: There never are adaptations in physiology, requiring any special analysis, where there are only complications or even apparent deviations from the purely physico-chemical type of events which are, so to say, statical, *i.e.* fixed in quantity or quality, however peculiar or typically complicated they may be; all such peculiarities indeed, may properly be called “adapted,” that is to say, very well fitted to perform a specific part in the service of normal general functioning, and they are “adapted” to their part by virtue of a certain “adaptedness” of the organisation; but they are not “adaptations” in any sense of the word. PRIMARY AND SECONDARY ADAPTATIONS IN PHYSIOLOGY We approach the subject of true adaptations, that is, of adapting processes, as soon as any kind of variation in functioning occurs which corresponds to a variation of any factor of the medium in the widest sense. But even here our work is by no means done by simply showing such a correspondence of outer and inner variations. We know very well already, from our former studies, that now we are faced by a further problem, that we are faced by the question whether we have to deal with simple primary kinds of adaptations or with the far more important secondary ones. As the discrimination between primary and secondary regulations proves indeed to be of first-rate importance, you will allow me, I hope, to summarise our chief analytical statements regarding them in a most general form. We call primary regulatory any kind of morphogenetic or functional performance, which, by its very intimate nature, always serves to keep the whole of organisation or of functions in its normal state. We call secondary regulations all features in the whole of morphogenesis or of functioning which serve to re-establish the normal state after disturbances along lines which are outside the realm of so-called normality. This analytical discrimination will help us very much to a proper understanding of physiology. But before we turn to apply our definitions to actual facts, another preliminary problem has to be solved. ON CERTAIN PRE-REQUISITES OF ADAPTATIONS IN GENERAL