PREPARATION OF THE SUBSTRATES 1/3 



function to fulfil, in the animal kingdom have common 

 properties in their structure. In spite of our favour- 

 able experiences we have not ventured generally to 

 recommend the use of animal organs. It is still very 

 difficult to find a proper balance amongst the contrarv 

 results of many observers, and were we to change 

 the type of substrate without sufficient experience, 

 we should arrive at still more divergent results. 

 This is the reason why it is particularly necessary to 

 use organs of the same species as that to which the 

 serum under investigation belongs, as well as those 

 of a different type. Only when it is established that 

 harmonious results are obtained ought we to be 

 satisfied with non-specific organs, and always under 

 the condition that no substrate is used which shows 

 definite pathological alterations. 



Means of Obtaining Blood Serum.- -Three condi- 

 tions have to be complied with. The serum must be as 

 poor as possible in diffusible substances which react 

 with ninhydrin, and this is attained by taking the 

 blood in a fasting condition. In all cases in which 

 the albuminous metabolism is very rapid, in cases of 

 disease which are accompanied by decay of the 

 tissues, as in the case of carcinoma, in cases of 

 absorption of exudates and transudates, in all purulent 

 processes, and lastly, in effusions of blood, the blood 

 always contains a larger quantity of such compounds. 

 The blood serum must further be absolutely free from 



