82 Intracellular Proteins [Sept. 



Investigation of the pyrimidins as a possible method of distinc- 

 tion has led Levene to conclude that all animal nucleic acids contain 

 three such bases, cytosin, thymin, and uracil, while plant nucleic 

 acids contain usually only two, uracil and cytosin. 



An interesting Suggestion by Robertson shows how the chemical 

 study of the protein molecule indicates possible Solutions of physio- 

 logical Problems. In cell division the problem is to account for 

 Separation of the nuclei. It is evident that during this process 

 nuclein is being formed rapidly. Lecithin is a probable source of 

 the PO4 for this material. Loss of this PO4 may result in the 

 transformation of the cholin residue into a cholin soap. This soap 

 would lower the surface tension in the equatorial plane and hence 

 account for the Separation of the nuclear parts. The proposition 

 is, of course more suggestive than conclusive. 



In spite of extensive investigation of the cleavage products the 

 problem of the actual configuration of any typical protein molecule 

 is still unsolved. A factor that makes the Solution still more diffi- 

 cult is the tendency of proteins to alter. A classical method for 

 preparation often results in an entirely unexpected product. In 

 recent preparations of histone in this laboratory I have encountered 

 some surprising anomalies in this respect. It must also be stated 

 that we are not even sure that our extracted products preexisted in 

 the cell plasma. As a result of extraction procedure they may 

 become as different as coagulated albumin is f rom soluble albumin. 



Condition of proteins in the cell. The last Statement suggests 

 to US the importance of knowing more of the physical State of cell 

 proteins. It has long been a question whether colloidal Solutions 

 exert any osmotic pressure. While the question is still unsolved 

 evidence seems to answer the question in the affirmative, although 

 such pressure is at best relatively slight. Hardy showed that 

 colloidal particles are electrically active. The question then arose 

 as to whether this was a function of the particles themselves or 

 due to impurities. The use of Osmometers permeable to salts 

 tended to clear up this point and with certain protein Solutions 

 osmotic pressure was definitely shown to exist when such Osmo- 

 meters were used. Lillie showed, however, that this pressure was 

 not simply a function of concentration and temperature but that 



