EFFECT OF CARBONIC ACID GAS. 148 
a scanty growth; while a third group, like the B. 
typhosus and B. prodigiosus, are not at all affected, 
growing equally well as in the presence of oxygen, 
and the liquefaction, even of gelatin, not being inter- 
fered with; only, on account of the lack of oxygen, 
there is no p'gment formation. Finally, a mixture of 
one-fourth air to three-fourths carbonic acid gas seems 
to have no injurious effect on bacteria which cannot 
grow in an atmosphere of pure CO,,. 
Sulphuretted hydrogen in large quantity is a strong 
bacterial poison, and even in small amount kills some 
bacteria. 
