19- SOURCES OF ERROR (iX THE PROCESS) 



(b) The Xinhydrin Reaction. In order to under- 

 stand the propositions that follow, we must be clear 

 concerning the fact, that blood serum always contains, 

 in varying quantities, substances which are to be 

 found within the peptone group, and therefore react 

 with ninhydrin. After a meal at which albumen 

 has been taken, the quantity of such substances 

 appearing in the serum immediately increases, in 

 consequence of which the blood must be taken during 

 a state of hunger. 



A great many experiments have been necessary 

 to determine what quantity of serum, in general, will 

 give off to the dialysate only so much of the 

 substances referred to, as is required for a negative 

 reaction with ninhydrin. An insufficient quantity of 

 serum must not be used, if the decomposition of the 

 organ's albumen is to be as complete as possible. It 

 has been found that, in general, 1*5 c.c. of the serum 

 may be used. It is obvious that, under certain 

 circumstances, an even greater quantity of serum mav 

 give off so few substances reacting with ninhydrin 

 that the reaction of the dialysate still remains negative. 

 Conversely it may happen that 1*5 c.c. of serum 

 alone will give a positively reacting dialysate, which 

 is the reason why a control test with serum alone is 

 absolutely essential. The latter test indicates whether 

 the serum in use answers the condition of not giving 

 off, of itself, a sufficiencv of substances to react with 



