Chap. XXV. CORRELATED VARIABILITY. 337 



According to Spinola and others, 37 buckwheat (Polygonum fago- 

 pyrum), when in flower, is highly injurious to white or white- 

 spotted pigs, if they are exposed to the heat of the sun, but 

 is quite innocuous to black pigs. By two accounts, the Hy- 

 pericum enspum in Sicily is poisonous to white sheep alone ; 

 their heads swell, their wool falls off, and they often die ; but 

 this plant, according to Lecce, is poisonous only when it growns 

 in swamps ; nor is this improbable, as we know how readily the 

 poisonous principle in plants is influenced by the conditions 

 under which they grow. 



Three accounts have been published in Eastern Prussia, 

 of white and white-spotted horses being greatly injured bv 

 eating mildewed and honeydewed vetches ; every spot of skin 

 bearing white hairs becoming inflamed and gangrenous. The 

 Eev. J. Eodwell informs me that his father turned out about 

 fifteen cart-horses into a field of tares which in parts swarmed 

 with black aphides, and which no doubt were honeydewed, and 

 probably mildewed ; the horses, with two exceptions, were ches- 

 nuts and bays with white marks on their faces and pasterns, 

 and the white parts alone swelled and became angry scabs. 

 The two bay horses with no white marks entirely escaped all 

 injury. In Guernsey, when horses eat fools' parsley (Mthusa 

 cynapium) they are sometimes violently purged ; and this 

 plant "has a peculiar effect on the nose and lips, causing 

 "deep cracks and ulcers, particularly on horses with white 

 "muzzles." 38 With cattle, independently of the action of 

 any poison, cases have been published by Youatt and Erdt 

 of cutaneous diseases with much constitutional disturbance (in 

 one instance after exposure to a hot sun) affecting every single 

 point which bore a white hair, but completely passing over 

 other parts of the body. Similar cases have been observed 

 with horses. 39 



We thus see that not only do those parts of the skin which 

 bear white hair differ in a remarkable manner from those bearing 



sr This fact and the following cases ss Mr. Mogford, in the ' Veterinarian/ 



when not stated to the contrary, are quoted in ' The Field,' Jan. 22, 1861, p. 



taken from a very curious paper by 545 



Prof Heusinger, in ' Wochenschrift fur 39" , Edinburgh Veterinary Journal/ 



Heilkunde,' May, 1846, s. 277. Oct. 1860, p. 347. 



VOL. II. „ 



