McOlklt^and an\> FiTZGKRALB —Photo-electric Discharge. 5 



withered nettle leaves plucked some days previously. They were cut up and 

 pressed in a mortar with cold distilled water. After filtration the liquid gave 

 an effect corresponding to ten divisions per minute on the usual scale. After 

 concentration to half its volume, the activity of the water was increased about 

 60 per cent. After standing for some time in the laboratory, the liquid was 

 passed through a Chamberland-Pasteur filter, and found to be still active. ' 

 Boiling with animal charcoal and filtering through ordinary filter paper was 

 found to remove the activity. 



We tried similar experiments with leaves of euonymus, ivy, and plane 

 tree, and we may quote the numbers for the first : — ■. 



Leaves in a natural state, taken fresh from shrub, Activity = 10 

 Cold water extract from leaves, . . „ = 30 



A freshly cleaned copper plate, . . „ -^ 100 



We were, therefore, able to get a photo-electric activity equal to 30 per 

 cent, of that of copper by pounding up leaves in a mortar with cold distilled 

 water. To obtain the active extract it is not necessary to break up the 

 leaves. We immersed leaves in cold water, taking care that the surface of 

 the leaf and the stem below the water were not broken or damaged in any 

 way. With prolonged immersion we have obtained an activity as high as 14 

 on our scale. With distilled water near the boiling-point greater values are 

 obtained, and the period of immersion may be short. Hot water poured over 

 leaves of shrub euonymus, allowed to cool, and then tested, gave 45 per cent, 

 of the activity of copper. The active liquid obtained in this way was found 

 to maintain its activity for weeks when kept in a closed vessel, but the 

 activity fell away to one-third of its value in a week when exposed to the 

 air. 



We have attempted to obtain very active water solutions by concentrating 

 weak solutions, but without any very marked success. 



The rate of fatigue of these water extracts was not so great as in the case 

 of the acetone extracts diluted with water. 



It will be noted how much the activity of the extracts obtained from 

 leaves by simply immersing them in water exceeded the activity of the leaves 

 in their natural condition. Different coloured chrysanthemums, which gave 

 a very small effect, as shown in the table above, were found to yield a water 

 extract with an activity as high as 10 per cent, of that of copper. 



