374 
Bacteria , their Nature and Function. 
long cylinders, homogeneous long threads, and even spiral forms. 
But by artificial cultivation by exact methods they can be shown to 
belong to one and the same species ; and it can also be shown that 
under particular conditions of cultivation the bacillus almost invari- 
ably shows itself as cylindrical and thread-like forms ; whereas 
under other conditions it assumes the character of cocci and ovals. 
Photographs which were shown gave an exact representation of 
these cylindrical and thread-like forms observed in early gelatine 
plate cultures ; later on, when the growth has proceeded for some 
days, and the gelatine has almost entirely become liquefied, the 
majority of the individuals are very short — either coccus-like or 
short ovals. 
It is on account of this unstable or protean character of its form 
that Hauser gave it the name of Proteus, and being the common 
microbe of putrid decomposition, he called it Proteus vulgaris. 
This organism, as a first and important action, peptonises 
albumin and liquefies and peptonises gelatine ; then this peptone 
is decomposed, yielding, amongst other substances, leucin, tyrosin, 
indol, skatol, phenol, and, further, ammonia. 
(b) Bacillus coli . — The normal inhabitant of the intestine of 
man and animals is another powerful albumin-decomposing microbe, 
but, unlike the proteus, it decomposes albumin without first con- 
verting it into peptone ; it therefore does not liquefy gelatine like 
the proteus ; it rapidly decomposes albumin, forming indol and 
allied bodies, and even ammonia. 
Bacteria causing Ammoniacal Fermentation of Urea. 
In connexion with these true putrefactive bacteria I must 
mention a group of bacteria which, though not strictly connected 
with decomposition of albuminous matter, play an important part, 
inasmuch as their action supplements that of the former, the 
group in question consisting of species which can change urea and 
allied substances into ammonium carbonate. This action is generally 
and justly considered of the nature of a ferment or hydrating 
action, like that of other organised ferments to be presently 
described. But we mention this group here because by changing 
urea into ammonium carbonate it prepares, in one sense, the way 
for the action of certain other bacteria which, by oxidising 
ammonia into nitrites and nitrates, are the direct food-providers 
for the vegetable kingdom. Urea and allied substances, as stated 
above, are the last products of albuminous metabolism in man 
and animals, and therefore form an integral part of the material 
destined for the soil in which the plants of our gardens and fields 
live and thrive. I showed at this stage one of the species of this 
group — for there are seveial — the Micrococcus urea; ; this is a 
coccus growing as a white staphylococcus, and forming connected 
masses in the natural or artificial culture media ; it does not 
liquefy gelatine, and grows extremely rapidly at higher tempera- 
tures. 
