SOURCES OF ERROR (IX THE PROCESS) 



insufficient layer of toluol, changes of temperature in 

 the incubator, and working in places where acid or 

 alkaline vapours are developed. 



These sources of error ought, properly, to occur 

 very seldom. 



On the other hand, the following point is often 

 overlooked. After the tube has been filled with the 

 organ, and the serum and the toluol have been added, 

 it is absolutely necessary to make sure that the whole 

 of the tissue is covered with the serum and toluol. 

 Should the slightest portion of the tissue project 

 above the toluol, it is then liable to decay in the course 

 of sixteen hours, and so become a source of serious 

 error. 



In conclusion, we will add the following supple- 

 mentary' details, which are not at present in general 

 use, because they are not considered as being abso- 

 lutely necessary. We may, instead of the control 

 with serum, use a control with organ + inactivated 

 serum. The serum is heated for thirty minutes 

 at a temperature of 60 C. This kind of control is 

 capable of indicating an insufficiently prepared organ. 



Starting with the idea that a certain Hmital value 



O 



must be present, in order to give a colour reaction 

 with ninhydrin, one might conclude that it would not 

 suffice to test the filtered water, in which the organ 

 was boiled, with i c.c. of ninhydrin solution. We 

 have therefore produced a solution of silk-peptone, 



