changes, however extreme they may be, in checking the multiplication of the 

 lung worm. 



A certain period of the year, which varies in different districts from July to 

 September, is found to be most favourable for the development of the lung 

 worm, and sheep and calves which are put on the pastures during the dangerous 

 period are almost certain to become infested. Generally, the beginning of 

 autumn is the time when the first signs of the invasion of the parasites appears, 

 and, judging from post mortem appearances, the characteristic symptoms are 

 not evident until the parasites are fully grown. 



An important class of parasites remain to be noticed the arthropoda, which 

 are distinguished, as the name implies, by joint extremities. Only two of the 

 four sub-classes into which arthropoda are divided are parasites to warm- 

 blooded animals, i.e., arachnida and insecta. The first include the very 

 extensive parasites of acari or mange mites, and the somewhat rare pentas- 

 stoma, which in the larval form inhabit the digestive canal, and when mature 

 are found in the respiratory passages, chiefly in the nasal chambers. Insecta 

 may become parasitic for a time in the mature form ; for example, the biting 

 and stinging winged insects may be quoted, but the larval forms of insects have 

 the widest range as parasites, inhabiting the skin and also the internal organs. 

 Under the name of bots or maggots, the larvae of certain flies which molest 

 horses, cattle, and sheep are well known. Some of the larvae, as for instance, 

 the warble grub, bury themselves deeply in the tissues of the skin, excite 

 inflammation and suppuration, and do great damage to the hide, which the 

 healing process does not suffice to repair. The larvae of the bot fly are 

 introduced into the digestive organs of the horse without any effort on the part 

 of the fly, which deposits the eggs on the legs, and from this position they are 

 transferred by the animal's own tongue and swallowed. When in the stomach 

 the larvae fix themselves into the mucous membrane, in which they remain 

 secure until they are in a condition to migrate to the outer world and assume 

 the chrysalis stage, and lastly, that of the perfect insect. 



The reader who has followed the description of the various classes of 

 animals and plants which play the part of parasites to higher organisms, will 

 have realised the importance of the subject of parasitism, not only in relation 

 to the lower animals which play the part of host to the parasite^ but, what is 

 perhaps of even greater consequence, its possible influence on public health. 



Some forms of parasites are undoubtedly capable of transmission from the 

 lower animals to man. Capsuled Tritchina spiralis, the cysts of the two forms 

 of tape worm, which are found in the intestines of the human subject. One, 

 the Taenia solium, which has its larval form in the flesh of swine, and the other, 

 the Tpenia mediocunnellata, the cystic form of which infests the muscles of 

 cattle in India. 



Among parasitic plants, the ringworm fungus is readily transmitted to the 

 skin of the human subject, and finds a congenial habitat, producing derange- 

 ments which are often difficult to correct. 



In the following articles the different parasites which attack the several 

 domesticated animals will be referred to more in detail, and with particular 

 reference to the circumstances which favour their invasion, the disturbance 

 which they occasion, and the means of cure. 



BESIDES THE PARASITES belonging to nematodese, which have already 

 been described as infesting the digestive canal of the horse, there are some 



