170 On Absorption. 



they are seen separated at equal distances from each other, 

 and being perfectly circular, show the most beantiful prismatic 

 colours when attentively examined with a good quarter inch 

 objective. The colours change with the distance of the objec- 

 tive from the discs, exactly as they do when a piece of 

 perforated zinc held in a beam of diverging light is looked at 

 through a lens, and the distance varies between the zinc and 

 the lens. The appearances presented I have here sketched, 

 and I wish to add, that I am indebted to my colleague. 

 Professor Wilson, for a great deal of information on this 

 curious subject of interference, and to Mr. Ellery, for having 

 taken a great deal of trouble to examine many specimens of 

 blood. 



4th. It follows, that the observer in his desire to succeed, 

 can lind almost any colour he is seeking for, and not in the 

 blood-disks alone, but in those microscopic globules at times so 

 abundant in the blood, according as the distance between the 

 disks and the objective is varied ; and as the red is the broadest 

 of these interference fringes, it and its complementary colour 

 green, are most readily seen. 



I have then to state, that a drop of blood from an animal 

 injected as above, gives no certain evidence of its presence in 

 either the white corpuscle, lymph, or chyle corpuscle ; at most 

 they are all very slightly tinged of whatever colour has been 

 injected. Thus, the red spot seen in the centre of the dried 

 disk, when in focus, is more brilliant when majenta has been 

 injected, but more than this I cannot say. I have never seen 

 the nucleus of the white and allied corpuscles tinged, 

 although I have experimented upon sucking animals, in 

 whose blood they are so abundant. 



It had been found by Dr. Roberts, that after the formation 

 of the *' pullulation," if magenta was applied, " the projec- 

 tions were found to take the dye strongly, and especially the 

 vesicular body within the hood." 



In order to determine whether the living corpuscles would 

 be similarly affected, 1 injected half an ounce of tincture of 

 galls mixed v/ith one and a-half ounce of warm water into 

 the peiitoneal cavity of a fowl. Within a very few minutes 

 our "feathered biped" showed symptoms of intoxication, 

 and for the space of an hour was ludicrously drunk, reehng 

 and staggering about, but rapidly recovered. 



During all this time he was passing tannin in his urine, as 

 was evidenced by testing with a solution of iron. It soon, 

 however, disappeared both from the blood and urine. 



