452 THE DISEASES AND DISORDERS OP THE OX. 



be directly guarded against by a considerable amount of know- 

 ledge. It is a not uncommon belief that healthy people and 

 animals are less liable to the attacks of these unwelcome in- 

 vaders than those who are in a weakened or debilitated state ; 

 but as a matter of fact the direct opposite of this is more 

 probably true. At any rate parasites are quite as likely to 

 attack healthy individuals as unhealthy ones. A young lady 

 with the bloom of health upon her cheeks is quite as liable to 

 catch the germ of a tapeworm, from caressing with too much 

 fervour a favourite dog, as would be the hard-working gardener 

 or groom, should he engage in the same pastime. The ox 

 which is fattening rapidly in the rich pastures, and has a 

 superabundance of health and vigour, is even more likely to be 

 singled out for the attacks of the warble-fly than is a less 

 healthy comrade. The best members of a herd of cattle may 

 be the first to be attacked by, and the first to die as a result of, 

 cattle-plague, just as also the well-nourished of the human 

 family have been at times the most seriously afi'ected by typhus 

 fever. 



As everyone knows, animals live directly or indirectly on 

 the members of the vegetable kingdom, and hence they are 

 dependent upon plants, inasmuch as they cannot do what plants 

 can do, viz. derive their nutriment from the inorganic constituents 

 of the air and soil. This primary necessity, that animals 

 should be helped by the vital activities of plants, is the best 

 and most important instance of the intimate connection which 

 subsists between the two great kingdoms (as they are called) of 

 living organisms. This particular dependence may certainly be 

 looked upon as one of mutual advantage ; but, notwithstanding 

 the benefits accruing from this, and very many other like 

 instances of division of labour among living beings, it must 

 not be overlooked that the kind of inter-dependency which is 

 shown in parasitism is very generally a source of serious danger 

 and disturbance, and even death, to the higher animal at whose 

 expense the uninvited guest takes up quarters, and furnishes 

 itself with board and residence, free of cost. 



There are numerous kinds and degrees of parasitism. Some 

 instances of plants which live parasitically on other plants, and 

 also on animals, will readily present themselves to the mind. 

 The dodder attaches itself to plants such as the flax or clover. 



