116 THE AGUE PLANT. 



It is not necessary to possess more than a short selection of 

 my tests to include general purposes, and in some particular cases 

 a single test will be sufficient. 



I now pass to the remaining part of the subject, viz., Distortion, 

 which I believe is not so well understood, simple as it is. For 

 this test I rule a slip of glass with fine black lines, and place it 

 upon the stage, I then rule a disc with black lines and drop it 

 upon the diaphragm of the eye-piece. If the disc be not in focus 

 I turn back the screw of the eye-piece glass, or if this be not suf- 

 ficient I shift the diaphragm until I get my focus. I then bring 

 the lines on the stage into focus, and parallel with the eye-piece 

 lines. If the objective shall be found to have the usual distortion, 

 it will instantly be seen that although the central stage line is 

 straight and perfectly parallel with, and covered from the top to 

 the bottom of the field by the central eye-piece line, yet the other 

 stage lines bend their ends in a curvi-linear direction from the 

 centre of the field. Upon moving the stage the line that appeared 

 straight assumes the circular form, and one of the bent lines gets 

 into the centre and assumes its straight appearance, and so on, at 

 every motion of the stage. 



Upon one occasion, working with a fifth, I was puzzled by a 

 distortion of a kind I could not understand, and a distortion I had 

 never before noticed. Upon resorting to my tests I found the 

 lines bent not from their centre, but straight and parallel through 

 half the lower part of the field, and through the upper three- 

 quarters of the field they spread out like the feathers in the crest 

 of the Prince of Wales. I then knew that the lens (perhaps by 

 a blow or fall), had become displaced, so as to destroy its 

 parallelism. 



I shall be glad if discussion may evolve any better Tests. 



The Ague Plant.* 



Some years since I became interested in the statements of Dr. J. 

 H. Salisbury, of Cleveland, Ohio, in reference to the germs of 

 ague. Dr. Salisburyj* believes to have discovered the malarial 

 essence in the cells of certain Palmelloid plants. Desiring to in- 

 vestigate the subject, I sought for the plants described by him, in 



* From "Grevillea" No. 6, 1872. 



t See American Journal of Medical Sciences, 1866. 



