586 



TOLERANCE OF POISONS. 



It is a well-known fact that certain substances, poisonous under 

 ordinary circumstances, become less so when partaken of frequently 

 in moderate and gradually increasing doses, so that the longer the 

 habit is kept up, larger and larger quantities may be taken without 

 the ordinary poisonous effects appearing. A tolerance of the poison 

 is thus established, as in the case of opium-eaters, who by taking 

 this drug habitually for special purposes become so used to it that 

 they hud it necessary to continually increase the dose in order to 

 attain the same result. At length a dose that would have been fatal 

 at the commencement may be taken without any immediately 

 serious consequences. There is no lack of evidence tending to 

 show that such a tolerance of the bush poisons may be acquired by 

 animals feeding on them. By nibbling at these bushes while grazing 

 on their ordinary food, they may advance from a small quantity to a 

 larger, especially if their proper food becomes less plentiful ; and 

 their systems may be gradually inured to the poison, and a tolerance 

 of it at length reached. Whether, like the opium-eater, the domestic 

 or wild animals derive special enjoyment from their consumption or 

 the poison-plants, or acquire such an inordinate craving for them as 

 to tempt them to take more and more till their health is ruined, is 

 not so evident. The following facts support the view that animals 

 may acquire an immunity from the effects of the bush poisons : 

 (i). Travelling or imported stock, new to the district, are more 

 frequently poisoned than those stationed near the poison plants ; 

 (2). Wild horses and some cattle may graze amongst poison without 

 any ill effects ; (3). The flesh of wild animals when killed and eaten 

 by dogs and cats sometimes poisons them, though not when cooked. 

 Before accepting these statements as conclusive, however, the 

 sagacity of animals in avoiding the poison, and the possibility of 

 some portion of the plants themselves, contained in the stomachs of 

 those eaten, being consumed along with the flesh, have to be taken 

 into consideration. Differences in the degree of virulence of 

 poisonous plants are also known to exist in other countries 

 according to locality and season. A striking illustration or 

 tolerance, as narrated by the Hon. A. R. Richardson, if 

 correctly observed, would appear to show that some forms 

 of animal life may be indifferent to the poisonous principles. 

 The carcase of a poisoned goat was buried, and as it 

 decomposed the maggots creeping from it were devoured by 

 fowls, that sickened and died in consequence. In this case 

 the maggots, being born and bred among the poison, seemed 

 to have acquired a tolerance of it, and at the same time 

 to have been so saturated with it as to convey a fatal dose into 

 the system of the fowls. Mr. K. R. Parker, in referring to the 

 eradication of the box poison, says : " If fed off by sheep when first 

 it springs up it will never shoot again." The suggestion that sheep 

 should be turned in to feed on the young shoots of this virulent 



