120 



Scientific Proceedings (34). 



caderas by a single injection of trypanred acquired an immunity 

 that lasted 50 days. Another mouse cured of surra of Mauritius 

 by acetylatoxyl and " CI " had a strong immunity. In the 46 days 

 that followed treatment it received eleven inoculations of virulent 

 surra of Mauritius trypanosomes but did not become infected. 

 When next tested for its immunity (31 ith day), it was apparently 

 hypersensitive to infection. It was killed in 8 days by a greatly 

 attenuated surra of Mauritius strain. The attenuation was appar- 

 ently due to long continued passage through guinea pigs. One of 

 the two controls inoculated with this virus died on the twentieth 

 day. The other carried the trypanosomes for 1 1 1 days, recov- 

 ered spontaneously, and is still alive (184th day). 



64 (402) 



The leucin fraction of proteins. II, 

 By DONALD D. VAN SLYKE and P. A. LEVENE. 



\_From the Rockefeller Institute for Medical Research, Nezu York.'\ 

 In a previous communication' we have described a method for 

 quantitatively separating leucin and isoleucin from valin, the leucin 

 isomers being precipitated as normal lead salts. It has since been 

 found that from the specific rotation of the mixture of leucin and 

 isoleucin, as obtained analytically pure from the lead salts, the 

 percentage of each can be accurately calculated. The rotation 

 of d-leucin in 20 per cent, hydrochloric acid is + 36.8°, of 

 1-leucin + 15.6°. Consequently the proportions are calculated 

 by the formulae : 



, . , . 100 — 15.6) 



per cent, d-isoleucin = , 



^ 21.2 



^, . 100(36.8-7?) 



per cent, d-leucm = 



^ 21.2 



{R representing specific rotation in 20 per cent, hydrochloric acid). 

 The specific rotations of the isomers are unaffected by the boiling 

 acid used for hydrolysis, but are affected by boiling with alkalies. 

 Consequently the method is not applicable to products of alkaline 

 hydrolysis, which however is seldom used. 



These Proceedings, 1909, vi, 54. 



