CHAP.X. — MORPHOLOGY OF THE BACTERIA.— ENDOS POROUS 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 

 described below were carried out in the 

 summer-temperature of an ordinary room, 

 that is, not much above or below 2o~ C. 



This species forms small rods 2-5 <x 

 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 

 unequal parts, which again grow to rods of 

 the size above mentioned (Fig. 194 a, b). 

 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 



Fig. 194. Bacillus Megateriitm. a outline of a motile 

 chain of rods in active vegetation, b a pair of motile rods in 

 active vegetation, p a quadricellular rod in the state of b 

 after treatment with alcoholic solution of iodine, c a five- 

 celled rod in the first preparation for forming spores. ^-^/" 

 successive stages of a pair of rods while forming spores, d 

 about two o'clock in the afternoon, e about one hour later, 

 /"an hour later than**. The spores in formation inyare 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 iny 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. g 3 the same 

 about four o'clock. h\ two spores with the walls of the mo- 

 ther-cells dried and then placed in a nutrient solution about 

 forty-five minutes after eleven. h> the same about half- 

 past twelve. 1, k, /later stages of germination as explained 

 in the text. ?•< a rod formed from a spore placed eight hours 

 before in a nutrient fluid and in the act of splitting trans- 

 versely, n magn. 250, the rest of the figures 600 times. 



application of desiccating and colouring re- 

 agents, alcohol and tincture of iodine for 

 example, shows that the rods even in this 



state consist of short members which become twice as long as broad or a 

 tittle longer, and then divide by the formation of a transverse septum into two 

 members (ft). 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. 



