PREPARATION OF THE SUBSTRATES 



blood, whilst organs freed from blood and subjected 

 to parallel tests were left unattacked. This funda- 

 mental rule, of completely freeing the organ in ques- 

 tion 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 pan- 

 creatic gland, then in most cases a ' decomposition J 

 would be found. Such mistakes are avoided bv 



/ 



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 thvroid Hand would not 



J O 



be decomposed by Basedow serum, while a gland 



