1888.] Toxic Principle of the Aroideaa. 115 



and leaves (which we also proved to be highly active when applied to the 

 tongae) on a pig, a rabbit, and a guinea-pig, but with negative results. 

 Although we took the precaution to starve these animals before giving 

 them the leaves and tubers, there is a considerable doubt in our minds 

 whether the rabbit and guinea-pig ever ate any of the arum ; the pig 

 certainly did eat a small portion of a leaf, but, although it must have 

 been very hungry, it refused a mess of chopped tubers, bran, and sugar. 

 There is thus in these experiments some uncertainty. We were parti- 

 cularly anxious to try the effect of the fresh tubers on a pig, because we 

 had the very circumstantial note from the Civil Surgeon of Dibrugarh, 

 in which it is stated that two pigs had been killed by eating some of the 

 same tubers as those with which we had experimented. 



A rough analysis of the ash indicated the presence of a large amount 

 of potassium and magnesium ; calcium was also present, but we failed 

 to obtain indications of sodium. The acids consisted of carbonic, 

 phosphoric, and hydrochloric, with traces of sulphuric acid. We also 

 obtained from the dried tubers very marked quantities of potassic nitrate, 

 so that when they had been incinerated they behaved very like tinder, 

 containing salt-petre. The examination of the ash thus failed to afford 

 us any clue to the physiological action of the fresh tubers. 



It now occurred to us that possibly the painful effects produced by 

 arum when in contact with the tongue &c. might be due to mechanical 

 causes. A microscopic examination of a section of a tuber revealed the 

 presence of very numerous bundles of needle-shaped crystals ; and we also 

 found similar crystals in the leaves and stems. These crystals were seen 

 under the microscope to be insoluble in cold acetic acid, but easily soluble 

 in cold diluted nitric or hydrochloric acid. Caustic potash was without 

 action. A tuber was boiled, and sections made when cold ; on micros- 

 copic examination crystalline bundles were still visible. The presence of 

 raphides in the cells of plants is well known ; even in the arum they 

 have been before observed. Dymock mentions needle-shaped crystals in 

 the parenchyma of the A. sylvaticuni ; and in the nettle tribe stalked 

 crystolithes have been described suspended in the cells. But, as far as 

 we are aware, the significance of these needle-shaped crystals in the 

 arum has not hitherto been recognized. There appears to us to be no 

 reason to doubt the fact, that the whole of the physiological symptoms 

 caused by arums are due to these needle-shaped crystals of oxalate of 

 lime, and that the symptoms are thus due to purely mechanical causes. 

 Bearing in mind the action of reagents on calcic oxalate, the reason why 

 mere boiling the tubers in water failed to deprive them of their activity 

 is explained by the insolubility of oxalate of lime in water. Again, the 

 action of dilute acetic acid, even at a temperature of 100° C, in slightly 



