THE PRESIDENT'S ADDRESS. 209 



in this matter, and from what opposite standpoints authors have 

 attempted to classify parasitic forms of life. 



A parasite is denned in Jameson's edition of Johnson's diction- 

 ary as being " one that frequents rich tables and earns his welcome 

 by flattery." This probably corresponds with the derivation of the 

 word from Tapa, beside, and oItos, food, but it does not appear al- 

 together applicable to a Tcenia or an Ichneumon. Jenkens' lexicon 

 comes somewhat closer to our notions ; it states a parasite to be 

 " a hanger-on ; a plant or animal living on another." These 

 probably are not works in which we should expect to find any great 

 scientific exactness ; let us therefore see what have been the 

 opinions held by those who have endeavoured to regard the matter 

 from a strictly scientific basis. General works on parasites are not 

 numerous, yet there are some to be found, although they are chiefly 

 confined to the parasites of man. Saint-Fargeau, one of the earlier 

 writers, says, " The parasite is he who lives at the expense of 

 another, eating his host's property but not his host." This has a 

 certain quaint resemblance to Johnson's idea, but if such was ever 

 the received view it has been somewhat widely departed from. 



" Parasites," says Kiichenmeister, " are independent organized 

 beings, descended from peculiar animal or vegetable patents, which 

 require, in order that they may be enabled to complete their de- 

 velopment, growth, or reproduction, to take up their abode, either 

 constantly or temporarily, in or upon a second animal or vegetable 

 organism of a different kind from which they derive their nourish- 

 ment.' 1 This definition is getting very close to the ordinary idea, 

 but it scarcely seems quite consonant with the fact that Kiichen- 

 meister appears to treat bed-bugs, fleas, blow-flies, gnats, and mos- 

 quitoes, as parasites of man. 



Van Beneden, in his well-known work, which is still probably the 

 best on parasites generally, does not put his definition in any single 

 sentence, but his opinions are evidently exactly opposite to those of 

 Saint-Fargeau ; he says, " Those creatures which merit the name 

 of parasites feed at the expense of a neighbour, either establish- 

 ing themselves voluntarily in his organs or quitting him after 

 each meal like a leech or a flea." It is evident that Van Beneden 

 does not consider a creature to be parasitic unless it does eat its 

 host; but he considers that it must not kill him, at all events not 

 at one meal ; those which do not eat the host he calls " mess- 

 mates," or " inutualists ; " thus, according to him, a leech, a flea, 



