Finally, the behaviour of fatty products was tested. In this case difficulties of method were encountered at first. The experiment made to ascertain the decomposition of fat in the blood, by simple titration of the acids produced, failed entirely. The question, whether, after the introduction of fats that are out of harmony with the body and the plasma, an increase follows of the amount of lipase in the plasma, could only be attacked after Michaelis and Rona had selected the alteration of surface-tension during dissociation as the basis of a method for the study of the decomposition of fats. The fats belong to a group of substances that are strongly surface-active, while the products of disintegration produced by their decomposition, such as alcohol and fatty acids, possess no marked influence over surface-tension. If plasma of a normal animal be mixed with any kind of fat, such as tributyrin, and the mixture be allowed to flow from a capillary tube, a certain number of drops escape in a given time. But if any fat gets into the animal's circulation by whatever means, then the number of drops escaping through the capillary tube decreases.
As far as we can judge from the experience gained up to the present, it seems that the conditions met with in fats are much more complicated than in the case of proteins and polysaccharides. This experience tells us that while, under normal conditions,
