ABDERHALDEN'S SERODIAGNOSIS OF PREGNANCY 261 



THE OPTICAL METHOD 



In the dialyzation method, we establish the transformation of a 

 colloid into a diffusible crystalloid; in the optical method we start, 

 for purely technical reasons, not with the whole protein molecule, but 

 with a peptone prepared of placental protein. The unsplit protein it- 

 self cannot be used, as this will interfere with the determination of the 

 rotation of the mixture of substratum plus serum. Further, in such 

 mixtures precipitation may occur and render the readings difficult. 

 Instead, we transform the protein into peptone, and observe the final 

 changes in the tube of the polariscope. 



Placental Peptone. This requires considerable care in its prepara- 

 tion. Placental peptone may be purchased of the Hochst Farbwerke, 

 and is expensive. Each specimen should be tested and its rotation de- 

 termined, as otherwise uncertain and unreliable results may be secured. 

 According to Abderhalden, a peptone may be prepared as follows: 



The tissues are first cut into small pieces and thoroughly washed until they are 

 white, as in the preparation of tissues for the dialyzation method. 



The tissue is freed of any excess of water by pressing it through several layers of 

 filter-paper, and the process of hydrolysis is begun. If a larger quantity of the same 

 tissue is to be collected, the pieces are prepared as they are secured by washing them 

 free from blood, boiling in water for ten minutes, and preserving in a stock jar con- 

 taining sterile water and chloroform, and covered with toluol. The tissues are boiled 

 in order to destroy the cell ferments and to prevent autolysis. 



The tissues are now weighed, placed in a large flask, and treated with three 

 volumes of cold 70 per cent, sulphuric acid. The flask is well shaken and carefully 

 stoppered, and placed aside at room temperature (not higher than 20 C.) until the 

 tissues have gone into solution. The flask is shaken occasionally. Solution is 

 usually completed within three days. The flask is now placed in iced water and 

 treated with 10 volumes of distilled water added slowly so that the temperature 

 does not rise above 20 C. 



The sulphuric acid is now precipitated with pure crystallized barium hydroxid 

 until the solution gives no precipitate with either the hydroxid or sulphuric acid. 

 A precipitate of a barium salt of peptones may appear in spite of the fact that no 

 sulphuric acid is present. This precipitate is soluble in nitric acid, whereas barium 

 sulphate is not soluble. The neutralization point is controlled with litmus paper. 

 Small portions are then filtered through filter-paper and tested, first with barium 

 hydroxid and then with sulphuric acid. If a turbidity develops on testing with the 

 barium hydroxid, nitric acid is added and the whole gently warmed. If the pre- 

 cipitate persists, it is evident that more barium sulphate should be added. The 

 final neutralization is effected with dilute sulphuric acid and barium hydroxid. 

 When the solution is free from sulphuric acid, the precipitate of barium sulphate is 

 secured by filtering through filter-paper or by centrifugalization. It is then worked 

 up in a mortar with distilled water and again filtered. It is well to repeat this wash- 

 ing once more. 



The peptone solution is now concentrated in a special apparatus that permits 



