The following observation is important. If albumen is injected into the circulation of an animal for the first time, defensive ferments are found to appear, in the case of intravenous injection, at the end of about one day. If the injection is repeated, say, a month after the defensive ferments have disappeared, then the ferments reappear very much earlier. (Abderhalden and Schiff.) May it not be that immunity partly rests upon the fact that an organism is able to set free its defensive ferments quicker than usual?
Syphilis, also, may certainly be studied from the standpoint we have laid down. We have to consider the affected tissue on the one hand, and the spirochæte on the other, as substrates.
It is also clear that we may suspect the presence, in the serum, of defensive ferments which are able to reduce fats, carbohydrates, nucleo-proteids, &c. The demonstration of proteolytic defensive ferments represents only one special case. We have selected this case because, up to the present, no methods exist for satisfactorily demonstrating lipolytic or amylolytic ferments—in short, those ferments which are directed against the particular constituents we have mentioned—unless one has rather large quantities of serum at one's disposal. We are, meanwhile, engaged in extending our researches to other ferments.
With regard to the infectious diseases, we should
