252 SUMMARY OF CURRENT RESEARCHES RELATING TO 
in the image. All other tissues, whether containing chlorophyll or not, 
are impermeable to these rays. 
Demonstration of the Evolution of Oxygen by Diatoms.* — Mr. 
T. 0. Palmer has succeeded in demonstrating the absorption of carbon 
dioxide and the elimination of oxygen by diatoms experimentally by the 
following process, dependent on the property of hematoxylin of assuming 
a yellow colour with a tinge of brown when absorbing C0 2 , while, in 
the presence of nascent oxygen, the red hue gradually deepens, finally 
becoming a deep blood-red. In the apparatus here figured (fig. 20), 
the dish is filled up to the line D E with water tinted with a freshly 
made solution of luematoxylin, sufficient to stain it a pale red. The 
tube A is then filled with the same solution, stopped with rubber, through 
which is passed a quill tube, and the tube suspended, the very fine end 
of the quill dipping into the water. Another portion of the hematoxylin 
Fig. 20. 
solution is acidified by C0 2 from the lungs, blown into it through a 
glass tube, till it assumes a brownish-yellow tint, and the tubes B, C, 
prepared in the same way, are filled with this solution ; living diatoms 
{Eunotia major ) having been placed in tube C. The apparatus is now 
exposed to bright light, preferably to direct sunlight. Gas arises from 
the diatoms in tube C, and simultaneously the colour of the liquid, 
which is at first like that in B, begins to change. Within 15 minutes 
the colour has again become almost or quite as red as that in tube A. 
The C0 2 has now, in large measure, disappeared from the solution. The 
action continues, and the colour in tube C deepens rapidly, showing oxi- 
dation, and this action continues until the colour is blood-red. Still 
more striking results are obtained as follows : — In tube A is placed a 
living snail ; in B live diatoms ; C being left for comparison. Under 
the influence of sunlight, in the course of a few minutes, A pales 
* Proc. Acad. Nat. Sci. Philadelphia, 1897 pp. 142-4 (1 fig.). 
