90 On Coloured Vision produced by Santonine. 



up the Santonine and deposits it in crystals when the liquid is 

 allowed to evaporate in the open air. Some time afterwards, 

 Tromsdorff junior submitted Santonine to a very careful and 

 complete study, and gave a new method for preparing it. This 

 method is now generally adopted. It consists in mixing 

 4 parts by weight of the dry semen contra with 1£ parts of 

 caustic lime, and extracting the mixture three successive times 

 with 16 to 20 parts of strong alcohol. The liquid thus obtained 

 is distilled until reduced to 12 or 16 parts. It is then filtered 

 to separate some flocconous matters which are deposited. The 

 filtered liquid now contains only Santonine and lime; for 

 Santonine acts as an acid, and combines easily with soda, 

 potash, lime, etc. It is evaporated to half its volume, mixed 

 while hot with an excess of acetic acid, and allowed to cool, when 

 Santonine crystallizes abundantly. It may be carefully washed 

 with a little alcohol, and then crystallized again. By dissolving 

 it in alcohol, bleaching the liquid by adding a little animal char- 

 coal, and filtering, perfectly pure Santonine is obtained, in the 

 shape of flat, six-sided prisms, quite colourless and odourless. 



As Santonine is insoluble in water, or nearly so, it has no 

 taste unless it be masticated for some time, when a slight 

 bitterness is perceived. Its solution in alcohol has, however, 

 a very bitter taste. It is fusible, and can be sublimed to a 

 certain extent ; but if the temperature be rather high, it in- 

 flames and burns with a bright smoky flame. Its best solvent 

 is alcohol ; ether and essential oils dissolve it likewise, and 

 fixed oils also take up a little ; but it is very slightly soluble in 

 water. Its specific gravity is 1*247. 



As regards light, Santonine possesses peculiar properties ; 

 it refracts light very strongly, like the diamond or like quartz ; 

 and when exposed for a few minutes only to the direct light of 

 the sun, the white crystals turn to a brilliant yellow, which be- 

 comes rather darker if the action of the sun's rays be continued 

 for any length of time. As this change only occurs upon the 

 surface of the crystals, and forms a very thin layer of yellow 

 matter, which protects the inside of each crystal from any further 

 change, the composition of the substance appears to remain the 

 same ; but if the action of light were caused to continue until 

 the whole mass of the crystals was changed into this yellow 

 substance, I have no doubt the latter would be found to differ 

 in more than one respect from the original Santonine. 



Santonine is prescribed, more particularly by German phy- 

 sicians, as a vermifuge for children ; but we have many reasons 

 for supposing that its action in this respect is less efficacious 

 than that of the plant, the semen contra, or Barbotine itself. 



The most curious property of Santonine is certainly its phy- 

 siological effect upon the vision. Experiments were mado upon; 



