POISONOUS PLANTS 271 



red, a point which appears to sharply distinguish the other- 

 wise nearly parallel cases. 



Besides gastro-enteritis, there is acute nephritis, the kidneys 

 being greatly enlarged, and the urine dark, albuminous, 

 free of sugar, and bloody. 



Causation. — The only known agent of poisoning by acorn, 

 oak and beech is tannin, whose general action is that of an 

 astringent. In overdoses it proves dangerous, probably by — 



(1) gastric disturbances, due to precipitation of proteins ; 



(2) astringency, causing constipation ; (3) dysentery, follow- 

 ing on constipation. The immunity of certain animals to 

 acorn, and the existence of a large number of different 

 natural tannins, and the enormous doses required to induce 

 dysentery, are obstacles in the way of this explanation. It 

 has been suggested that specially active forms of tannin, or 

 unrecognisable active principles, may be responsible, but 

 positive evidence is lacking. It is noteworthy that the 

 drinking of tanning ivaste liquors sometimes causes harm, 

 probably from similar causes, and at present the commonly 

 accepted explanation of the disorder, as one due to acute 

 digestive derangement^ is the best. 



The chemical recognition of tannin in fluids is easy. The 

 tannin may be separated from acid aqueous extracts, and 

 recognised by the dark coloration with ferric chloride, and 

 by the precipitation by tannin of gelatine and of alkaloids 

 from solution. 



The leaves, fruit, and twigs of Hawthorn, Cratcegus 

 Oxyacantha, are sometimes eaten by sheep, and may also 

 cause death by gastric derangement. Usually there will be 

 found very densely impacted masses of the plant on post- 

 mortem examination. 



Fern Poisoning-. 



The root of the male fern (Aspidiumjilix-mas) contains 

 about 8 per cent, otjilicic acid and also JUimar one, a neutral 

 substance. Pilicic acid is a widely used and effective agent 

 against tapeworm, and may act as a poison. 



