STERILIZATION AND DISINFECTION. 189 
cell. It becomes larger and more refractive, and its outer wall becomes 
firmer and thicker. It may be said, in other words, to have changed 
directly into a spore. But few observations of this process have been 
noted, and some authorities doubt the existence of this form of sporu- 
lation. 
How are spores affected by different conditions of temperature and 
by dryness ? 
Some varieties seem to possess the power to retain their vitality for 
an indefinite period, both when kept dry or when exposed to cold. 
They retain life at higher temperatures than do the mature bacteria, 
and when dry are able to withstand a higher degree of temperature 
than when in a moist condition. 
How do bacteria sometimes become self-destructive ? 
They may die from the action of deleterious material produced by 
themselves. The mature bacteria are more susceptible to these influ- 
ences than are the spores. Then, again, they may in a confined space 
be completely starved out from an exhaustion of the supply of their 
necessary nutriment. Here, again, the spores may remain in a passive 
state and resume their activities when more favorable conditions are at 
hand. 
In what part of the bacillus does the spore develop ? 
It may develop in the centre or at either end. At the point of 
development there is an enlargement of the bacillus, and when this is 
situated in the centre of an organism it gives rise to a spindle-shaped 
body. When formed in the end of an organism it may give rise to a 
club-shaped body, or, as it has sometimes been compared, to a drum- 
stick-shaped body; hence the name, drummer bacillus. 
STERILIZATION AND DISINFECTION, 
What is sterilization ? 
It is the process by which every micro-organism is destroyed in or 
upon the material that is to be rendered absolutely sterile and free from 
bacterial life, 
In what ways may this object be attained ? 
By the application of heat, both in the dry and moist forms. Also, 
these minute organisms may be destroyed by the application of certain 
chemical agents which hinder their powers of development. 
