ARE NOT TRUE PARASITES. 235 



derived never do they give origin to descendants 

 having such properties and powers. On the other 

 hand, every parasite is complete as an organism, 

 and gives rise to organisms like itself, which may 

 repeat its life history. A parasite possesses indi- 

 viduality, but a disease germ can no more be 

 regarded as an individual than a white blood cor- 

 puscle, or a pus corpuscle, a nail, a hair, or a gland 

 follicle can be so considered ; for, from any of these, 

 under no known circumstances can a complete 

 individual organism be developed. If such bodies as 

 mucus corpuscles, pus corpuscles, cancer cells, tubercle 

 corpuscles, and disease germs generally, be termed 

 parasites, the nails, or hairs, or glands, or limbs might 

 with equal propriety be regarded as of this nature. 

 Even the brain cells have been spoken of as parasites, 

 but one would have thought that if any part of the 

 body of a man belonged to him his brain cells were 

 certainly his own, and therefore could not be parasites 

 living upon him. Such confusion has resulted, that it 

 is really difficult to decide what is a parasite ; and 

 it seems almost vain to hope to restore the scientific 

 meaning of a term which has been entirely metamor- 

 phosed by the sparkling wit and keen satire of 

 transcendent literary genius. 



Nature of Contagious Disease Germs. Although 

 many diseases are caused by the action of noxious 

 gases, fluids, and solids of various kinds, every one will 

 agree that the particular forms of disease now under 



