240 Ellis . — The Life-history of Bad l his hirtus. 
rapid, or if the colonies were planted too close together, the whole plate 
becomes suffused with a uniform homogeneous layer, and often this 
homogeneous layer is the first indication of growth that is obtained. 
In this particular culture I saw the most prolific formation of spores 
that I have ever witnessed. Every available spot had been used up for 
this purpose. In some cases, some of the individuals had lengthened 
without dividing : in these, the spores were arranged very close together, 
often as many as 6-9, so closely packed together that the cell would have 
found it impossible to find room even for another half spore (Fig. 12). 
It thus seems as if, in the case of Bacillus hirtus , a plentiful supply of 
oxygen influences favourably the formation of spores. The formation 
of spores, however, must be due to more than one factor, for in another 
Agar-plate which I set, under approximately the same conditions, there 
were no spores, but all the individuals were extremely motile. After 
forty-eight hours, however, the motility had been lost, and spore-formation 
had commenced. It was not, however, as profuse as in the former culture. 
It will be seen later, that in an Agar-tube growth the formation of spores 
usually takes place after three days, so that the conditions under which 
growth takes place in an Agar-plate expedite the formation of spores. 
I consider that spore-formation is the result of the sum total of at present 
unknown external circumstances. In order to test the effect of the absence 
of oxygen on spore-formation, cultures were grown in Buchner’s anaerobic 
tubes. Apparently the formation of spores was not influenced by the 
absence of air. This subject was not pursued any further, as it was beyond 
the scope of this investigation. 
There are two characteristics of Bacillus hirtus Agar-plates, which, 
though not invariable, yet may help in diagnosing the species. The first is 
that, as was pointed out to me by one of my students, Mr. Pettigrew, the 
Agar often appears partially liquefied. It never extended so far as to 
liquefy completely the whole of the medium, but a distinct liquid film was 
formed on the surface, after which growth and also liquefaction appeared to 
cease. It is probable that a ferment was secreted which dissolved the 
Agar, but that later other secretions acted as a deterrent to further action 
of the ferment. 
The second characteristic is that occasionally the Agar-plate cultures 
take on a deep bronze colour. When the colonies are first formed, they 
possess the normal white colour, but occasionally the deep bronze colour 
appears. The conditions of the formation of this development were also 
not further investigated, but it is probable that slight peculiarities in the 
constitution of the Agar may have contributed to this peculiar growth. 
When I inoculated from a bronze colony on to an Agar-tube, I found that 
at first a fleshy crinkled white growth appeared on the surface. This, 
after three days, assumed a bronze colour at the top, which gradually 
