494 LIFE-HISTORIES 
ing its sugar into lactic acid. Such decomposition, in which 
the products are not offensive, is distinguished as fermenta- 
tion. Both fermentation and putrefaction are regarded as 
due to the action of enzyms (comparable to diastase) which 
are secreted by the active organisms concerned. The tuber- 
culosis bacterium is another species especially noteworthy 
as it is the germ of ‘‘consumption”’ in man and other animals, 
producing various forms of the disease according to the part 
of the body in which it develops. An organism which 
thus feeds upon the substance of another living thing is called 
a parasite;? the organism which supports it being termed 
the host. Bacteria capable of producing the disease often 
occur abundantly in the sputum of tuberculous patients, and 
if this dries small bits are readily detached and blown about. 
A sufficient number drawn into the lungs or getting into the 
blood of a susceptible host give rise to the disease. Hence 
the wisdom of isolating tuberculous patients to avoid con- 
tagion, and the importance of enforcing the regulations of 
Boards of Health against all spitting in public places. Direct 
sunlight being soon fatal to the plant in all its stages, affords 
a most valuable means of preventing infection, and often 
of effecting a cure by killing the parasite. 
Nearly all contagious diseases are caused by fission fungi, 
and to the micro-organisms or ‘‘microbes”’ of this same class 
are due almost every sort of putrefaction, fermentation, and 
decay. The discovery of this important truth has given a 
new significance to cleanliness, and a knowledge of their 
life-histories and peculiar properties affords a scientific basis 
for methods of preventing or regulating the activities of 
these excessively minute, yet exceedingly powerful agents 
of change. While some forms of bacteria are a menace to 
health others are useful in important ways as in the manu- 
facture of butter and cheese, in the retting of flax and other 
fibers, and as improving the soil for many farm-plants. 
The various forms assumed by the cells and colonies of 
fission fungi may all be closely matched by forms of blue 
‘ Fer’-men-ta’tion < L. fervere, boil, be agitated. 
? Par’a-site < Gr. parasitos, one who eats at another’s table, a hanger 
on; < para, beside; sitos, food. 
