CHAP. X.—MORPHOLOGY OF THE BACTERIA.—ENDOSPOROUS BACTERIA, 463 
All the above phenomena are in themselves sufficiently simple, and ‘their 
course is essentially the same in all the species; but it is nevertheless desirable 
that we should study a few examples more closely, and see in what light the 
parts in question present themselves and the form which the specific differences 
assume. 
Our first example shall be the large species long known in our laboratories by 
the name of Bacillus Megaterium. This exceedingly instructive form (see Fig. 194) 
was first observed in boiled cabbage-leaves used for the cultivation of Myxomycetes 
and species of moulds, and was afterwards studied in pure cultures in water or gelatine 
mixed with 7-10 per cent. of grape sugar and a small quantity of meat-extract and 
also in a pure 2-3 per cent. solution of 
meat-extract. The gelatine is liquefied by 
the Bacillus. Most of the cultures to be a? 
described below were carried out in the Sy 
summer-temperature of an ordinary room, = 
that is, not much above or below 20° C. 2 
This species forms small rods 2-5 p» 
in thickness and cylindrical in shape with 
the ends rounded off. The rods, which 
do best when obtained from spores, grow 
rapidly in a fresh nutrient solution where 
they have no competitors to disturb them, 
and become usually 4-6 times longer than 
they are broad; then they separate by trans- 
verse division into two halves or into two 

FIG. 194. Bacillus Megaterium. a outline of a motile 
chain of rods in active vegetation. 4 a pair of motile rods in 
active v i pa i rod in the state of 5 
after treatment with alcoholic solution of iodine. c a five- 

unequal parts, which again grow to rods of 
the size above mentioned (Fig. 194 a, 4). 
A single rod floating in the solution usually 
appears in these circumstances even under 
high magnifying power to be unsegmented, 
and to be filled with a slightly refringent 
protoplasm in which only a few separate 
granules can be distinguished. But the 
application of desiccating and colouring re- 
agents, alcohol and tincture of iodine for 
example, shows that the rods even in this 
celled rod in the first preparation for forming spores. d-f 
successive stages of a pair of rods while forming spores, ¢ 
about two o'clock in the afternoon, ¢ about one hour later, 
Jan hour later thane. The spores in formation in /are ripe 
towards evening; no others were formed, the one which . 
apparently began to be formed in the third cell from the top 
in d and e has disappeared ; the cells in / which did not con- - 
tain spores perished by about nine o’clock in the evening. 
r a quadricellular rod with ripe spores. gl a five.celled : 
rod with three ripe spores placed in a nutrient solution 
after several days’ desiccation, half-an-hour after noon. 
g? the same specimen at about half-past one. g3the same 
about four o'clock. 4, two spores with the walls of the mo- ‘ 
ther-cells dried and then placed in a nutrient solution about 
forty-five minutes after eleven. 42 the same about half- | 
past twelve. z, 4, / later stages of germination as explained 
inthetext. “arod formed from a spore placed eight hours" 
before in a nutrient fluid and in the act of splitting trans- 
versely. a@ magn. 250, the rest of the figures 600.times. 
state consist of short members which become twice. as long as broad or a 
little longer, and then divide by the formation of a transverse septum into two 
members (2). The transverse septa are extremely delicate when young, but when 
the water is withdrawn by a reagent they and the lateral wall stand out clearly 
distinguished from the shrunken protoplasm. Older transverse septa swell to a 
greater thickness in the living individual, and acquire at the same time a soft 
gelatinous consistence; this causes the transverse splitting of the longer rods men- 
tioned above, the pieces remaining loosely coherent or separating entirely from one 
another, according to the relation between the cohesion of the jelly and the . forces 
from without which promote a separation. ’ 
