Ellis . — The Life-history of Bacillus hirhts . 239 
1. Any relation between size of colonies and time of growth. 
2. Any relation between time and liquefaction of the gelatine. 
3. Any diagnostic characters based on irregularity of growth of the 
colonies. 
With regard to No. 3, the round or oval form of the colony is often 
departed from, and even in the same plate there is often considerable 
diversity of structure. The chief external factors which influence the 
growth on the gelatine are the following : — 
1. Temperature. 
2. Crowding or otherwise of the colonies. 
3. Percentage of water in the nutrient gelatine. 
With regard to Bacillus hirtus , under all circumstances, the colonies 
are first noticeable as minute grey specks, which in course of time liquefy 
the gelatine. In addition it may be stated, that usually the colonies 
become extremely irregular, and that very often the superficial colonies 
show a granulated appearance and vary in thickness from the centre to the 
periphery, the thickness being greatest at the centre and least at the 
periphery. In most cases this results in the formation of a ‘ nucleus * 
at the centre, leading down to the periphery by means of stratified layers. 
Less often growth is characterized by the formation of irregular threads or 
bands stretching out from the surface, which is well described by Henrici 
as ‘blitzahnliche Auswiichse.’ 
Agar-plate Cultures. 
A culture was made from an inoculation taken from a growth in an 
Agar- tube which was one day old. After fifteen hours at 3 2° C. there was 
a splendid growth. The superficial colonies ranged from mere specks 
up to the diameter of 1 mm. The larger colonies were well raised from 
the surface and white in colour. Under the microscope ( x 80) each 
appeared as if made up of threads densely packed together. At the edge 
a clear transparent line bounded the colony. Under higher magnification, 
the individuals are seen to be motile, and almost invariably consisted 
of two cells joined together as in Fig. 11, evidently indicating that all 
the cells were rapidly dividing, and that separation took place as soon 
as the wall had been formed. I take this to be the surest sign, that 
the conditions of growth are very favourable. In this culture every 
individual was motile. The demonstration of the cilia is given in the 
paragraph on the motility of this form. The colonies under the surface 
were much smaller, uniformly opaque with a ragged edge, sometimes 
thrown out into jagged promontories. After twenty-four hours, some of 
the colonies were from 2-21 mm. in diameter, and very much raised from 
the surface. As they get bigger they often lose their round outline,, 
becoming somewhat wavy. If the growth on the plate has been very 
