158 



ISOELECTRIC POINTS OF PROTEINS 



extremely high acidity of the ripened lemon might be brought about 

 in some such way.^^ 



The lack of homogeneity of tomato juice that has merely been 

 squeezed through cheese cloth is manifest. It contains, however, 

 nearly 1 per cent of protein. Filtering the juice removes a large 

 amount of this protein and at the same time appears to decrease the 

 hydrogen ion concentration of the filtrate to nearly 10~^n. Whatever 



TABLE V. 

 Measurements on Tomato Juice. 



the explanation of the latter observation, the removal of protein by 

 filtration is easily understood. Protein exists largely in suspension. 

 In entire conformity are the results of cataphoresis (Table V). 

 The unfiltered juice usually migrates to the cathode. A slight reduc- 

 tion in acidity reverses the sign of the protein. The protein, there- 

 fore, exists near its isoelectric point and probably sKghtly on the acid 



^^ Hempel, J., Compt. rend. trav. Lab. Carlsberg, 1917, xiii. 



