278 SCIENCE PROGRESS 



given by the conductivity method. Thus in the case of a 

 deci-molar solution the respective values are 0*843 an d 0*925. 

 Further it will be noticed that the 7 values continue to fall 

 steadily as far as they have been determined, i.e. up to one- 

 molar, but that the a values fall to a minimum at about half- 

 molar, thereafter increasing rapidly, passing through unity 

 and ultimately rising to 2*228. What the actual physical 

 meaning of this may be, it is difficult to say. (To be continued.) 



ORGANIC CHEMISTRY. By P. Haas, D.Sc, Ph.D., St. Mary's 



Hospital Medical School. 

 In a lecture delivered recently before the Chemical Society, 

 Prof. Hopkins chose for his subject " Newer Standpoints in the 

 Study of Nutrition," and some of the more important points 

 dealt with are contained in the following summary. 



The protein molecule is not absorbed by the body as such 

 and all processes of oxidation or molecular reconstruction are 

 preceded by a complete hydrolysis into amino acids. The 

 proof of this is two-fold ; in the first place examination of the 

 blood of anaesthetised animals before and after a meal shows 

 that nitrogenous food is conveyed by the blood to the tissues 

 mainly in the form of amino acids, and secondly, it has been 

 repeatedly shown that animals may be kept alive on a diet of 

 amino acids as their sole source of nitrogenous food, and that 

 young animals will grow on the same diet. Furthermore, if 

 proteins such as albumoses or peptones which we consume in 

 ordinary food are injected into the blood-stream, they are 

 rapidly excreted by the urine, showing that they are foreign to 

 the blood, whereas amino acids injected into the blood-stream 

 are metabolised quite normally. In starvation the life of the 

 animal is maintained by drawing upon the tissue proteins for 

 its supply of nitrogenous material, but here again, on examining 

 the blood, one finds not the unchanged tissue proteins, but the 

 amino acids arising from these by hydrolysis by means of 

 autolytic ferments. 



The fact that the animal is able to maintain itself on an 

 amino acid mixture enables one to ascertain experimentally 

 the relative value of individual amino acids and whether certain 

 amino acids are indispensable to life or are possessed of any 

 particular function in nutrition by virtue of their molecular 

 structure. In all experiments in which animals are fed on 



