190 Mr. Porter and Dr. Edridge-Green. Negative After -Images 



The intravenous injection of heated venom, even in the amount of 

 1*1 mgrm. per kilogramme of body weight, was found to be without effect 

 upon rabbits ; examination of sections of the lungs and also of the liver, 

 spleen, kidney, and heart muscle of animals killed half an hour after 

 injection failed to reveal any separation of fibrin in the blood-vessels. A 

 control experiment, in which 0"73 mgrm. per kilogramme of body weight was 

 injected in the course of one minute, caused death at the end of 30 seconds. 

 The behaviour of heated venom, when injected into the blood stream, is 

 thus seen to be consistent with the conclusion that the coagulant is a 

 thrombin. 



Summary. 



The different mode of action exerted by thrombin and thrombokinase upon 

 circulating blood plasma is described, and it is shown that the coagulant of 

 viper (JEchis carinattis) venom, as exhibited by its effect in causing intra- 

 vascular separation of fibrin when injected into the blood stream, and also 

 indicated by its behaviour when heated, is a thrombin and not a 

 thrombokinase. 



Negative After-images and Successive Contrast with Pure 



Spectral Colours. 



By A. W. Porter, B.Sc, F.R.S., Fellow of University of London University 

 College, and F. W. Edridge-Green, M.D, F.B.C.S. 



(Received March 31,— Read November 13, 1913.) 



In a recent paper* Prof. Burch has criticised our results on " Negative 

 After-images and Successive Contrast with Pure Spectral Colours."f 

 Prof. Burch suggests that the change in blue and violet obtained after 

 fatigue with red light may be explained on the Young theory, if the stray 

 light, which we stated was present, be taken into consideration. He states 

 that the reason, on this theory, why the violet appeared bluer and darker 

 after fatigue to red was due to the elimination of the red component in 

 the stray light. 



In consequence of this criticism we have since repeated our experiments, 

 taking the most minute precautions to exclude stray light by covering the 



* 'Roy. Soc. Proe.,' 1913, B, vol. 86, p. 117. 

 t ' Roy. Soc. Proc.,' 1912, B, vol. 85, p. 434. 



