230 
A hderhalden's Reaction 
to this method are the technical difficulties involved in measuring the 
rotation of the light in the solutions employed, and it is only capable 
of application in specially equipped laboratories. 
(2) The second method depends upon the fact that the molecules 
of albumins and polypeptids are too large to pass through an animal 
membrane, but the pores of the latter are not sufficiently fine to prevent 
the passage of peptones. 
In order to employ this dialysing method, a piece of the organ to be 
employed is mixed with the serum under examination, and the mixture 
put into a dialysing capsule and dialysed in distilled water for about 16 
hours. The dialysate is then tested for the presence of peptones, and 
if these are found it is evident that the serum must contain some pro¬ 
teolytic ferment, or ferments, acting upon the particular organ employed. 
In applying this method to the diagnosis of pregnancy, the serum of 
the woman to be examined is mixed with a piece of placental tissue, 
the mixture dialysed for 16 hours, after which the dialysate is examined^ 
for peptones, the presence of the latter denoting that the woman is 
pregnant. 
Up to the present time more than 3000 tests have been made by 
this method and in every case a positive reaction was found to be a 
sure sign of pregnancy. In the Quick Laboratory, we also have 
examined the blood from a number of cases, kindly supplied to us by 
Dr Roderick, and obtained uniformly positive results with the sera of 
pregnant women. 
In order to apply this test successfully, however, it is necessary to 
work very exactly, as there are many sources of error. 
The serum to be tested must be quite clear and without any trace 
of haemoglobin. It is best to take the blood from a vein by means of 
a dry needle, and to collect it in centrifugal tubes. The blood is then 
left at room temperature for three to six hours, in order to let the clot 
separate out, and afterwards the serum is well centrifuged in order to 
remove all red blood corpuscles. If any of the latter are left in the 
serum they are dissolved during the dialysis, and as a result the haemo¬ 
globin passes through into the dialysate and interferes with the reaction. 
The blood should be collected before meals, preferably before 
breakfast, as during the process of digestion the serum always contains 
more or less peptone. For this reason when performing an experiment 
it is always necessary to make a control employing serum alone, to see 
whether it contains any dialysable substances which give the Ninhydrin 
reaction. 
