April 3, 1920.] Agricultural Gazette of N.S.W. 267 



to chocolate colour, and watery extracts are a yellowish red. The cause of 

 the trouble in animals is said to be a red fluorescent substance which renders 

 the skin very sensitive to light. The usual colouring matter or pigment in 

 skin is able to protect it against the injurious action of the sun even thougli 

 it is sensitised by the substance mentioned, but unpigmented or white skin 

 being devoid of such protection suffers accordingly. Other plant sub- 

 stances than St. John's Wort produce this peculiar sensitisation of 

 unpigmented skin to sunlight, for example, certain clovers, buckwheat, and 

 the common wild trefoil so prevalent in parts of New South Wales. For 

 detailed reference to the latter the reader is referred to an article by the 

 writer (S. D.) in the Journal of Comparative Pathology, entited " Trefoil 

 dermatitis, or the sensitisation of unpigmented skin to the sun's rays by trefoil 

 ■{Medicago denticidata)." It would appear that the condition produced by these 

 plants as the result of their ingestion may be referred to the presence in them of 

 an agent, in some cases still undetermined, which reacts to sunlight. It is 

 evident, however, that the condition produced by St. John's Wort is far 

 more severe in its systemic and local effects than that induced by the other 

 skin-sensitising plants. 



The infested area in New South Wales which occasioned this article is about 

 5,000 acres, with a few other small scattered areas throughout the same 

 district. The pest has been known in the locality for about twenty or thirty 

 years and is slowly spreading. The larger area mentioned is now thickly 

 infested. Some of it is in very hilly country where it would be difficult 

 to deal with ; but a good deal is in cultivated situations, where some owners 

 are trying to eradicate it from their land whilst neighbours are doing nothing. 

 In other places, again, it is seen along watercourses or on the sides of roads. 



Stock usually are reluctant to eat it and will only readily do so when 

 there is little else to eat ; though when the plant is young and before 

 flowering they appear to have less objection to it. This is confirmed by the 

 feeding experiments to be referred to later. The condition resulting from 

 feeding on St. John's Wort is seen at any period of the year, but the plant 

 appears to produce its greatest effects when in the flowering stage. Some 

 state that when it is young, animals eat it with impunity. It is also stated 

 that with sheep, if they eat only a small proportion of the plant in its flowering 

 or most active sta,ge, with plenty of other grasses, no ill effects are observed. 

 My experiments, however, show that an amount small in proportion to the 

 -daily weight of food consumed by a sheoip will, if eaten daily, produce 

 pronounced symptoms. In the district referred to, the animals principally 

 affected are sheep and cattle, but very occasionally horses also suffer. It 

 is stated that human beings have developed sores on their legs after walking 

 through a paddock containing St. John's Wort, and on their hands after 

 handling the plant. In view of the mode of action of the plant these 

 statements require more evidence before St. John's Wort can be accepted as the 

 cause of the trouble. The view that animals become affected merely by ~ontact 

 with the plant and not by eating it also needs confirmation. Animals of any 

 •age are affected. 



