128 Drs. H. Chambers and S. Kuss. Action of [May 1, 



adhere firmly ; they may be repeatedly washed and then stained without 

 being freed. 



If the blood be not incubated, clotting is delayed, and the motion of the 

 leucocytes to the surface considerably prolonged ; this is of importance in 

 the following experiments : — 



A drop of blood was placed on a clean piece of mica, sufficiently thin 

 to allow easy penetration of the a-particles. It was covered with a watch- 

 glass and placed on the radium capsule, the radiation from which was 

 screened in such a manner that it was entirely confined to a square window 

 of about 1*5 sq. mm. On placing the mica sbeet over the capsule, therefore, 

 the drop of blood was not radiated by the «-rays except the area which was 

 directly above the small window. 



After an exposure of about 20 hours at room temperature the clot was 

 removed, the mica surface washed with saline, and stained. The resulting 

 picture was as indicated by fig. 3. 



It is seen that in a region corresponding to the radiated area there is an 

 almost complete absence of leucocytes ; the area free of leucocytes is, 

 however, slightly greater than that of the window, the ratio determined by 

 a magnified projection on squared t paper being T34 : 1. This increase is 

 probably due to cross firing of the rays. A different result was obtained 

 under the following circumstances : — 



A drop of blood was shed on to a thin mica sheet, covered with a watch- 

 glass, and incubated for 1J hours. This ensures a plentiful supply of 

 leucocytes on the mica surface. 



The system was removed from the incubator and placed over the radium 

 capsule, which was again provided with a small square window, of area 

 1 sq. mm., through which came the a-rays. After an exposure of about 

 20 hours at room temperature, followed by the usual staining process, the 

 picture presented was as shown in fig. 4. 



Inspection showed that the area free of leucocytes was much larger than 

 that of the window. A measurement similar to that already described gave 

 the ratio 2 - 8 : 1. In this experiment numerous degenerate leucocytes were 

 observed in the radiated and surrounding zones. 



If therefore the a-radiation proceeds during the slow migration of the 

 leucocytes out of the clot to the mica at room temperature, the area free 

 of leucocytes practically corresponds to the aperture through which the 

 rays come. If, however, the leucocytes are first allowed to make their way to 

 the mica surface, part of which is then radiated, the area free of leucocytes, 

 is found to be much larger than that of the radiated area. 



The different results in these two experiments indicate that in the former 



