May, 1912.] 



427 



Live Stock, 



be clean. Farmers who have a herd 

 affected with a disease which is not 

 contagions sometimes move to supposed 

 clean farms, either hiring the grazing 

 or selling the herds outright. If some 

 of these animals have acquired the taste 

 for the particular plant they will hunt 

 for it, and if they find it in sufficient 

 quantity will eat of it and become 

 affected ; in this way the disease may 

 " spi ead." 



This abnormal craving may be acquired 

 through scarcity of feed in winter or 

 early spring, which causes the animals 

 to eat anything green. If they are 

 moved to a farm where the feed has 

 not been eaten down closely, they are 

 likely to find enough of their normal 

 food to make it unnecessary to resort 

 to the dangerous species, and so the 

 losses may be checked for a certain time, 

 only to recommence, however, when 

 the veld is eaten down. In such cases 

 an obvious method of treatment is the 

 provision of an adequate supply of palat- 

 able winter feed such as Teff hay. This 

 would act as a preventive, but not as 

 a remedy for cases where the poison 

 has already been taken into the system. 



A Distaste may also be Acquired.— It is 

 commonly stated by men who are much 

 with stock in South Africa that animals 

 learn to know and to avoid poisonous 

 plants. Certain it is that stock brought 

 up on a farm where Tulp abounds will 

 feed among it constantly and with 

 impunity, often without the loss of a 

 single head, while strange animals, from 

 places where it does not grow, will eat 

 of it, and die if not carefully watched 

 and treated. Experiments carried out 

 by our Veterinary Division tend to con- 

 firm this view ; G. V. S. Dunphy (1906) 

 notes that sheep and goats which had 

 once been poisoned with Dichapetalum 

 and had recovered from the effects 

 seemed to show a great dislike for the 

 leaves. In a test with Yellow Tulp 

 (Homeria pallida) Doctor Theiler was 

 unable to induce a hungry ox which had 

 been starved for thirty-six hours to eat 

 Tulp even when chopped and well mixed 

 With hay, 



Small amounts of Foison may some- 

 times be taken with Impunity— It does 

 not necessarily follow that a plant is 

 harmless because stock are occasionally 

 seen to eat of it without injurious effect, 

 for large doses may be fatal. Some 

 deadly poisons (e-g., Strychnine, Bella- 

 donna and Aconite) are valuable drugs 

 when taken in official doses. 



Many stock farmers of the Transvaal 

 are firmly convinced that the converse is 

 also true, and are prone to give decoc- 

 tions of Tulp or Gift-blaar to render their 

 cattle and horses immune. 



Classification. — Vegetable poisons may 

 be grouped as follows, if we adopt 

 Robert's classification of poisonous 

 substances :— 



1. Irritants which cause gross anato- 

 mical changes of the organs, e.g., croton 

 oil and savin. 



2. Blood poisons— 



(a) which interfere with the circulation 

 in a purely physical manner, e.g., 



ricin and abrin ; 



(b) which dissolve the red corpuscles, 



e.g., the saponins ; 



(e) which, with or without primary 

 solution of the red blood cor- 

 puscles, produce in the blood me- 

 thtemoglobin, e.g., picric acid ; 



(d) which have a peculiar action on the 

 colouring matter of the blood or on 

 its decomposition products, e.g., 

 hydric cyanid. 



3. Poisons which kill without the 

 production of gross anatomical change— 



(a) which affect the cerebro-spinal 



system, e.g., strychnine morphine, 

 coniin, curarine, atropine, stro- 

 phine, aconitine, etc, ; 



(b) which effect the heart, e.g., digitalin, 



helleborin, muscarin. 



(lo be continued.) 



