blood, whilst organs freed from blood and subjected to parallel tests were left unattacked. This fundamental rule, of completely freeing the organ in question from its blood, is often transgressed. If the serum does not contain any defensive ferments against the form-elements of the blood, then, of course, even an organ containing blood may give correct results. As, however, mistaken results are liable to occur, such an organ should, as a rule, never be used.
It is advisable never to use one particular organ exclusively for testing a definite problem; and one should always work with controls. For instance, placenta is always tested with serum from obviously non-pregnant persons. Male serum should also be employed. Should cases of diabetes, for instance, be tested exclusively with faulty preparations of pancreatic gland, then in most cases a "decomposition" would be found. Such mistakes are avoided by using thoroughly prepared organs on the one hand, and by means of control experiments on the other.
It is of fundamental importance to establish the morphological state of the organ used, and its origin. It is possible that, in a given disease, a normal organ is not decomposed, although the same organ is readily attacked, if it has already undergone particular pathological changes. Thus it is quite possible that, for instance, a normal thyroid gland would not be decomposed by Basedow serum, while a gland
