Aug. 3l 1 888.] 



SCIENTIFIC NEWS. 



109 



OUR KNOWLEDGE OF THE 

 BACTERIA. 



\\ TE have repeatedly had occasion to refer to the part 

 played by certain oi these minute beings in trans- 

 mitting diseases as well as in originating and keeping 

 up important changes both in living and lifeless matter. 

 It now strikes us that a more systematic description of 

 these beings — avoiding, of course, technical specialities 

 — may be interesting to not a few of our readers. For 

 this purpose we shall avail ourselves, to a considerable 

 extent, of a summary of " bacteriology," contributed to 

 our contemporary, Humboldt, by Dr. Carl Giinther, of 

 Berlin. 



The bacteria are the smallest living beings of which 

 we have any knowledge. They are very widely dis- 

 tributed in nature — a privilege which they owe to the 

 tenacity of their life, the simplicity of their vital condi- 

 tions, and,aboveall, to their extremely rapid multiplication. 

 If we wish to make their acquaintance we need merely 

 pour a little water upon some animal or vegetable sub- 

 stance — such as a bit of meat, a little hay, a few peas, 

 grains of rice, a crust of bread — and let the whole stand 

 over-night in a warm place. The water will be found 

 to have become turbid, and, if we examine a drop under 

 the microscope with a sufficiently high power, we shall 

 see a crowd of minute colourless beings of very simple 

 forms. Some of them have the shape of rods, varying 

 greatly both in length and thickness. In length they do 

 not exceed a few thousandth parts of a millimetre (a 

 millimetre, it will be remembered, is 39 hundredths of 

 an inch), whilst their breadth is measured only in the 

 ten thousandth parts of a millimetre. 



Besides the rods we find tiny globules, differing in 

 size, and, like the rods, sometimes occurring detached, and 

 sometimes in clusters or united in chains. All these 

 beings, which are at once distinguished by their minute- 

 ness from the yeast cells and moulds (which are much 

 bulkier), are called bacteria. The little rods are known 

 as bacilli, and the globules as micrococci. A third form 

 of bacteria, also to be found in infusions, though less 

 plentifully, appear as minute forms, either spirally curved 

 like a cork-screw, or as thin, short, curved rods, and are 

 known as spirillar and comma-bacilli. 



If we examine such a mixture of bacteria in a recent 

 infusion we see the individual specimens in constant 

 : motion. The bacilli and micrococci dance up and down, 

 .to and fro, but without any great change of place. This 

 j is merely the case of molecular movement, called pedesis, 

 or Brown's movement from its discoverer, and which is 

 'always observed in minute solid bodies suspended in 

 liquids. But in addition to this molecular movement, 

 which is common also to lifeless matter, many bacteria 

 are capable of independent motion. This is most dis- 

 tinct in the spirillas. They screw through the liquid with 

 the speed of an arrow, and then occasionally remain for a 

 time quiescent. Among the bacilli only certain kinds 

 are capable of independent motion, the remainder being, 

 (like the micrococci, stationary. The independent move- 

 ments of the creatures where they exist seem to be 

 executed by means of flagella — threads like a whip-lash 

 attached to the extremities of each. 



Their reproduction is effected ordinarily by fission. 

 \A single individual grows in length, becomes divided 

 transversely in the middle, and is thus resolved into two 

 individuals, each of which is again subdivided in a 

 similar manner. The parts, or the offspring, if we may 



so call them, may either entirely part company or they 

 remain connected together, forming ultimately chains or 

 links by continued fission. We then call them streptococci, 

 or chain-cocci. The bacilli form, in a similar manner, 

 threads. Sometimes bacteria, after fission, remain toge- 

 ther in heaps or clusters, apparently adhering together 

 by means of a cement. These clusters are known as 

 zooglcea. In some species of micrococci the fission takes 

 place not in one, but in two or three directions. Thus 

 we have groups of four cocci, forming a square, or bale- 

 shaped heaps each of eight cocci, or sarcina. Among 

 bacilli we sometimes observe under unfavourable circum- 

 stances, such as the exhaustion of the nutrient fluid, the 

 appearance of small, shining corpuscules, which are 

 formed within the body of the bacillus. These corpus- 

 cules, which are known as spores from their analogy to 

 the spores of fungi and algae, play a similar part to the 

 latter. They are discharged from the maternal body in 

 a shower, and are capable of remaining dormant, if 

 needful, until suitable nourishment is to be found. 



Dr. Dallinger, however, in his most recent researches 

 has established that the bacilli do not continue to repro- 

 duce themselves by fission, however favourable the 

 surrounding conditions. After a number of successive 

 fissions they seem to become exhausted, and form and 

 discharge a crowd of spores as just described. The 

 enveloping membrane, which is all that remains of the 

 primary bacillus, sinks to the bottom of the liquid, 

 apparently dead. 



The spores, set free, if they meet with suitable nutri- 

 ment, grow up to bacilli, and increase by fission as before. 

 (To be continued.) 



POISONS IN THE WORKSHOP. 



(Con/in ued from page jj.) 

 CINGULARLY enough, the compounds of the metal 

 chromium are often overlooked by writers on 

 poisons. Some of these substances are not less to be 

 dreaded than arsenic, whilst they are used on a very 

 large scale in the arts. .The most common form in 

 which chromium occurs in trade is as chromic acid 

 and its compounds with potash and soda. The bichro- 

 mate of potash forms splendid orange-red crystals, which 

 dissolve readily in water and possess an intensely dis- 

 agreeable taste. On this account, as well as from its vivid 

 colour, it is little likely to figure as an agent either in 

 malicious or accidental poisoning. The first danger con- 

 nected with this substance is in its manufacture. We 

 need not here describe the process, but the men em- 

 ployed are liable to suffer from perforation of the carti- 

 lage which divides the two nostrils, so that the cavity of 

 the nose becomes single. We do not, however, know 

 that the mischief ever spreads farther, so as, e.g., to 

 attack the palate. 



The use of this bichromate of potash in dyeing has its 

 perils. It is consumed to a vast extent in dyeing black 

 upon wool and woollen cloths, which are boiled along 

 with logwood and a certain quantity of bichromate. Of 

 course, the hands of the workmen often get splashed 

 with the liquor, especially when the goods are drawn 

 out of the dye-pans and spread out. Upon some men 

 the solution takes no effect. Others find their fingers 

 becoming swollen and inflamed, and if such continue at 

 this kind of work ulceration sets in, and the fingers or 

 the whole hand might be lost. In all the large dye- 



