PREPARATION OF THE SUBSTRATES 163 



manner in which a substrate is prepared is of the 

 greatest importance for the whole success of the 

 dialysation process, and, unless one adheres to the 

 directions in every particular, one is bound to meet 

 with unsuccessful results. These, however, can be 

 successfully avoided if the preparation of the sub- 

 strate be carried out with proper attention. The 

 principle of the matter is, to obtain substrates which 

 contain coagulated albumen and are absolutely free 

 from diffusible substances which react with ninhydrin. 

 We shall demonstrate the method of obtaining the 

 substrates by means of the preparation of coagulated 

 placenta. Other organs are treated in exactly the 

 same way ; only, those which are rich in fats and 

 lipoids have to be previously extracted with carbon 

 tetrachloride in a Soxhlet apparatus. The same 

 applies also to tubercle bacilli. Placenta can always 

 be procured in a fresh state, whereas in other cases 

 we have to deal with organs from dead bodies. In 

 the latter case the dissection should be made at the 

 earliest opportunity. The best corpses are those of 

 accidents. If prolonged agony has been undergone 

 previous to death, the organs are almost useless. 

 It is very important to test the organs for patho- 

 logical changes; and it is absolutely essential 

 to state in what condition the organ used was 

 found, for different results could easily be obtained 

 if one observed used normal organs while another 



