May 25, 1893] 



NATURE 



«3 



further improvement, it is nevertheless well established that a 

 considerable number of phenomena in nature are intimately 

 associated with bacterial life. The world of bacteria is com- 

 parable 10 an unseen flora which, in variety of character, of 

 activity and importance in llie economy of nature, compares 

 with the visible llora, and in itsextension and area of distribution 

 is as great as, in some respects greater than, that of the visible 

 vegetable and animal kingdom. Though unpreceived by the 

 unaided eye, this bacterial world forces itself, by its multifarious 

 activity, continually on our attention ; it comes into prominence 

 by the vast effects, the slow but far-reaching results which it 

 produces on man, animal, and plant, for good and for evil, in 

 life and in death. Some of these actions I shall have the honour 

 to bring before you this evening, and you will see that while 

 there are bacteria whose actions are undesired and not con- 

 ducive to the well-being of man or animals, there are others 

 which are of the greatest service both to them and to plants, 

 and are an essential and integral part in the economy of nature. 



I spoiie just now of the bacterial world as of an unseen flora ; 

 I meant by this a part of the vegetable kingdom not perceived 

 , by the unaided eye, though, as you will see, it is easily brought 

 to perception by a variety of means. The individuals that con- 

 stitute the bacterial world are, as is no doubt known to you, of 

 such extremely minute size that only by the aid of the microscope 

 can they be seen, their size being often less than ^^5^517 or 

 STTssij P!"t of an inch, rarely more than jsVcr part of an inch. 

 They are spoken of as having the character of plants, because the 

 elements, like those of a plant, are invested in a sheath of cel- 

 lulose, within which is contained the essential part, the living 

 protoplasm, the bacterial individuals being in fact comparable to 

 unicellular plants, in which, however, no definite cell nucleus has 

 been hitherto demonstrated. It ought, however, to be mentioned 

 that various observers have attempted to show, and, by complex 

 methods of staining, have succeeded in showing in some bacterial 

 species the existence of parts which resemble, and which are 

 considered as comparable to, the nucleus forming an integral 

 part of the typical vegetable cell. 



In speaking of bacteria as of plants there are other than 

 morphological characters which guide us in this designation ; 

 bacteria resemble plants in this essential, that they possess the 

 power to build up, out of simple organic compounds, the most 

 complex substances such as the protoplasm of their own bodies. 

 There are known not a few bacterial species which grow and 

 multiply, i.e. which build up their highly complex nitrogenous 

 alliuminous substances at the expense of relatively simple nitro- 

 genous bodies, such as ammonium tartrate, urea and allied sub- 

 stances, or wliich can do this even by the absorption of free 

 nitrogen of the air. Other species require for their growth and 

 multiplication as complex nitrogenous substances as the animal 

 body itself, and like this latter are capable of breaking them up 

 into simpler combinations. Pathogenic bacteria — many of the 

 species concerned in the decomposition and putrefaction of 

 albuminous substances — belong to this group. 



All bacteria multiply by division ; hence their name, schizo- 

 niycetes, or fission «fungi, the typical process of multiplication 

 consisting in the enlargement of an individual, and in subsequent 

 splitting into two by hssion, at the conclusion of which process 

 two new individuals are the result, each of them capable of en- 

 larging and again dividing in the same way into two, and so on. 

 but it can be easily shown by comparative observations and ex- 

 amination of suitably prepared specimens of artificial cultures 

 of the different species that not seldom the process of multiplica- 

 tion does not follow this line. 



I show you here a lantern slide of a microscopic specimen of 

 one of those species which, owing to the spherical or nearly 

 spherical form of the elements, is called a coccus, or micrococcus ; 

 and owing to the manner of growth in clusters and continuous 

 masses, is called a staphylococcus ; this microscopic specimen 

 has been obtained by the method of making " impression pre- 

 parations," that is to say, by means of a thin glass pressed on to 

 a recent, i.e. a young colony or colonies growing on the surface 

 of a solid medium, an exact impression is obtained of the growth, 

 and a good and correct insight is obtained of the manner in which 

 the colony enlarges, and the way in which the individuals con- 

 stituting the colony grow and multiply. You see in this photo- 

 graphic representation that there are a good many individuals 

 many times (4- 10 times) as large as others, that some of these large 

 elements are uniform, while others show just the indication of a 

 tr.insverse fissure by which the large element is dividing ; still 

 others show two fissures at right angles, by which the big element 



.becomes divided into four smaller ones. But you see also the 

 majority of cocci are only minute dots, some in pairs, others in 

 clusters, the former looking like two demilunes separated by a 

 straight clear line ; in fact, this latter appearance denotes the 

 typical manner in which one coccus, having first enlarged a little, 

 divides into two small elements. ISut the presence of the huge 

 elements mentioned above tells us also that one coccus may go 

 on growing to a very large size without dividing, and having 

 reached this huge diameter, then commences to divide, first 

 into two, then into four, eight, and sixteen individuals of the 

 typical size. 



I show you here an impression preparation ofa recent colony 

 of another spec\ti (Bacillus coli), the individuals of which are 

 rod-shaped or cylindrical, and arewhat are called typical bacilli. 

 Here the great majority of the individuals are of cylindrical 

 shape, and of a fairly uniform size ; a few only are shorter, and 

 arranged in the form ofa dumb-bell, indicating that one of the 

 longer individuals has by fission split up into two smaller indi- 

 viduals. But if you look at a third impression preparation, of 

 which I here show you a photograph (Proteus), you will see 

 that while there are a few chains of cylindrical bacilli, indicat- 

 ing successive division of the individuals and the new offsprings 

 remaining joined end to end — thus constituting what is spoken 

 of as a leptothrix — there are other threads in the colony which 

 either show a division into cylindrical elements only imper- 

 fectly or not at all, appearing uniform and unsegmented 

 threads ; where the segmentation is imperfect the individuals 

 are of very various lengths, some not longer than those typical 

 bacilli in the first-mentioned chains, others three and more 

 times as long. These appearances indicate that the multiplica- 

 tion of the bacilli does not always take place in that typical 

 manner in which it is generally represented, viz. one individual 

 elongates a little, then splits up into two short individuals ; but 

 a bacillus may go on elongating till it reaches the manifold 

 length of the typical rods, and having reached this great length 

 then segments into a great number of cylindrical rods. This 

 mode of multiplication can be made out not only in these im- 

 pression preparations, but can be actually observed in the fresh 

 condition under suitable conditions, e.g. on the warm stage. 



That this mode of growth appertains not only to cocci and 

 b.icilli, but also to the third morphological group of bacteria, 

 viz. the vibrios, or spirilla, is ascertained by the fact that often 

 one vibrio, i.e. a more or less curved rod-shaped individual or a 

 comma-shaped bacillus, grows into a uniform homogeneous 

 spiral or wavy thread, which is capable of splitting up into a 

 number, i.e. a chain of comma-shaped vibrios. 



We have then the typical mode of division, by which one in- 

 dividual, a coccus, or bacillus, or vibrio, as the case may be, 

 slightly enlarges, and then by fission divides into two ; or an 

 individual continues to grow to abnormal size or length,, and 

 then splits up into a series of individuals of the typical size ; 

 this latter mode of multiplication implies a deficiency of fission 

 for the time being, and is not, as far as can be made out, due 

 to any abnormal conditions affecting the growth, for in many 

 species this occurs in recent and active colonies under conditions 

 which in all other respects must be pronounced as favourable 

 for growth and multiplication. 



Another interesting appearance, shown by some species of 

 bacteria, is generally ascribed to degeneration or involution, i.e. 

 the bacteria assume peculiar abnormal shapes stated to be due 

 to abnormal influences, insufiicient or unfavourable soil, un- 

 favourable temperature, &c., &c. ; but while it is true that such 

 influences do produce abnormal shapes, disintegration, cS:c. , 

 there are certain changes in shape that are observed in somi; 

 species of bacteria while growing under perfectly favourable 

 conditions and with the normal rapidity, and which are anything 

 but degenerating. 



A recent colony of the bacillus anthracis, like the photograph 

 I show you here, growing on nutritive gelatine, is made up of 

 twisted and convoluted threads of cylindrical rods, which threads 

 are seen to shoot out and to extend like filaments from the 

 margin of the colony. Now, yoU' notice in the next photograph 

 that instead of these filaments being made up of the typical 

 cylindrical rods the former consist of relatively huge spindle- 

 shaped or spherical masses many times the diameter of the 

 typical rods. The threads of this colony are perfectly active, 

 and are growing with vigour and in perfectly normal circum- 

 stances as regards soil, temperature, and all other known con- 

 ditions. As a matter of fact, a few days later, as comparative 

 specimens show, all threads may be, and as a rule are, again of 



NO. 1230, VOL. 48] 



