OF THE CALABAR BEAN. 781 



Experiment CM. 



A portion of the web of a frog was arranged for microscopic examination, in the same way 

 as in the two preceding experiments. An artery and two branches (A, B, C) were selected for 

 examination, along with several adjoining pigment-cells. 



Before the application, A = 4;B = 2;C = 1'5: while the pigment-cells were in the stellate 

 form. 



A drop of a filtered, strong solution of extract was placed on the web. 



r Circulation more rapid ; 



In 5 minutes, A = 5 ; B = 2 ; C = 1-5. Pigment-cells \ with a few \ J hat were b , efore em P- 



ty now contain an ac- 

 tively moving blood 

 stream. 



concentrated, 

 with a fe\ 

 short rays, 



and many capillaries 



r in extreme 

 10 „ A = 5; B = 2; C = 15. „ < concentra- 



20 „ A = 5;B = 2;C = lo. 

 30 „ A = 5;B = 2;C = l-5. 



tion. 



J Circulation continues 

 ( active. 



» 



The action of physostigma on the calibre of the minute and contractile blood- 

 vessels is thus the reverse of that of atropia. 



Lister believes that the pigment-cells possess a nerve apparatus that governs 

 their condition in exactly the same way as the smpathetic ganglia and spinal 

 nerves govern the calibre-changes of the smaller blood-vessels.* If this be so, the 

 long continued concentration, which precedes the diffused condition of the pig- 

 ment in these cells, would imply that their nerves are more sensitive to irritation 

 than those of the vascular system, and that this pigmentary concentration is the 

 result of a stimulating property of the extract, of so slight a character as to 

 have no effect on the ganglia and nerves of the blood-vessels. 



When applied to the Eyeball, or to its immediate neighbourhood. 



As this investigation has been confined to the lower animals, the action on 

 the iris only can be here discussed. This has been observed in amphibia, reptiles, 

 birds, and mammalians. The pupil contracts within a few minutes after the 

 application of physostigma to the eyeball, to the cutaneous surface in its neigh- 

 bourhood, or to the nasal mucous membrane ; and, if the quantity have been 

 considerable, this may last for two or three days. It is caused much more 

 rapidly, and maintained for a much longer time, than the often varying state 

 of contraction that has been described as a symptom produced by physostigma 

 acting through the blood. There is no reason to doubt that it is as purely an 

 effect produced by contact with the iris as the opposite state that atropia 

 causes ; and so limited is the action, that in the same animal extreme physos- 



* On the Cutaneous Pigmentary System of the Frog; Philosophical Transactions, vol. cxlviii., 

 1858, p. 627. 



