266 FERMENTS AND ANTIFERMENTS 



forty-eight hours. If the serum contains a proteolytic ferment, the 

 peptone is split into amino-acids and the degree of rotation increased 

 from 0.05 to 0.5 and higher. This method requires an expensive polar- 

 iscope, considerable practice in making the observations and readings, 

 and is only reliable in skilful hands. 



THE DIALYZATION METHOD 



Testing the Dialyzing *Shell. The quality of the dialyzing shell 

 largely determines the success of this method. It must fulfil two re- 

 quirements : 



1. It must be absolutely non-permeable for albumin. 



2. It must be evenly permeable for the protein cleavage products, 

 such as peptones, polypeptids, and amino-acids. 



Special shells are made by Schleichter and Schull, No. 579a being 

 recommended at the present time. The shells must be of correct size, 

 and every one must be tested before being used. If a shell allows un- 

 cleaved protein to pass through, then all reactions would react posi- 

 tively regardless of the presence or the absence of the specific ferment. 

 If the shell is too thick and too tight, and prevents the passage of pep- 

 tones and ammo-acids, then all reactions would be negative, even though 

 the ferment were present in the serum and had digested the placental 

 protein. Accordingly, each shell must be tested and standardized, and only 

 those employed that have proved satisfactory. 



Glassware. It is highly important that all glassware should be 

 free from clinging particles or traces of albumin, acids, and alkalis. 

 Pipets and dialyzing cylinders should be washed in water, alcohol, 

 ether, and finally in distilled water, and sterilized by dry heat. Boiling 

 rods of solid glass (10 cm. by 0.5 cm.) should be washed in alcohol, 

 ether, and distilled water, wrapped in bundles of six in newspaper, and 

 sterilized by dry heat. 



A very convenient dialyzing cylinder is shown in the accompanying 

 illustration (Fig. 76). This cylinder measures 8 by 3 cm. It should 

 be plugged with cotton and sterilized. When the shell is loaded with 

 coagulated placenta and serum and covered with toluol, it will rest well 

 beneath the surface of the outside distilled water. The wide mouth of 

 the cylinder facilitates all manipulations and the shell cannot upset. 

 The apparatus is easily sterilized, and the cotton plug prevents bac- 

 terial contamination and undue evaporation of the contents. 



General Precautions. According to Abderhalden, the work should 



