FIG.

2. Torula cerevisia (after Rees).

3. Saccharomyces mycoderma, or oidium albicans, from an artificial cultiva

tion (after Grawitz).

4. Saprolegnia (after Sachs).

5. Oidium lactis (after Flügg ).

6. Fungi of favus, or oidium lactis (after Neumann).

7. Fenicillium glaucum (after Flügge).

8. Aspergillus niger, from a preparation mounted in glycerine.

9. Aspergillus niger, from the same preparation (Zeiss 1 o.i.).

10. Aspergillus glaucus (after De Bary).

11. Botrytis Bassiana (after De Bary

PLATE XXIX. (Facing page 384.)

1. Actinomyces (bovis).-From a section of a maxillary tumour in a cow. Stained by Weigert's method (orseille and gentian-violet). × 900. 2. From a section of the lung of a cow. The rosettes are much smaller, possibly owing to their being more confined by their surroundings than when growing in the soft pulpy tissue of the maxillary tumour. They are here shown with high amplification, but under a power of about 50 diam. (Zeiss A.A. Oc. 2) the section of a lung resembles miliary tuberculosis, and in the centre of a neoplasm the rosette appears about the size of a pin's head. Stained with Weigert's method (orseille and gentian-violet.) x 500.

PLATE XXX. (Following Plate XXIX.)

1. Actinomyces (bovis). From a section of a maxillary tumour in a cow. Stained by Plaut's method (magenta and picric acid). × 90. Note.--Neelsen's solution may be used instead of magenta solution.

2. Part of the same preparation, with higher amplification. The fungoid masses are very deeply stained by this method. The component clubshaped elements and their radiate arrangement are clearly shown. x 500.

PLATE XXXI. (Facing page 390.)

1. Actinomyces (hominis).—From a preparation of the grains from an actinomycotic abscess in a boy. Examined in glycerine. The drawing has been made of a complete rosette, examined by focussing successively the central and peripheral portions. Towards the centre the extremities of the clubs are alone visible; they vary in size; and if pressed upon by the cover-glass, give the appearance of an irregular mosaic. Towards the periphery the clubs are seen in profile, and their characteristic form recognised. At one part there are several elongated elements, composed of separate links. X 1200.

FIG.

2. Different forms of clubs from preparations in which the rosettes have been flattened out by gentle pressure on the cover-glass. × 2500.

(a) Single club.

(b) Bifid club.

(c) Club giving rise to four secondary clubs.

(d) Four clubs connected together, recalling the form of a branch of bananas.

(e) Mature club with a lateral bud.

(ƒ) Apparently a further development of the condition represented at (e). (g) Club with a lateral bud and transverse segmentation.

(h) Single club with double transverse segmentation.

(2) Club with oblique segmentation.

(j) Collection of four clubs, one with lateral gemmation, another with oblique segmentation.

(k) Club with lateral buds on both sides, and cut off square at the

extremity.

(7) Club with a daughter club which bears at its extremity two still smaller clubs.

(m) Club divided by transverse segmentation into four distinct elements. (n) Elongated club composed of several distinct elements.

(0) and (p) Clubs with terminal gemmation.

(2) Palmate group of clubs.

(r) Trilobed club.

(s) Club with apparently a central channel.

(t) Filament bearing terminally a highly refractive oval body.

PLATE XXXII. (Facing page 392.)

1. Actinomyces (hominis).-From cover-glass preparations of the fungus teased out of the new growths produced by inoculation of a calf with pus from a boy suffering from pulmonary actinomycosis. Stained by Gram's method and orange-rubin. The threads are stained blue and the clubs crimson. In the younger clubs the thread can be traced into the interior of the club. In some of the older clubs the central portion takes a yellowish stain, and in others the protoplasm is not continued as a thread, but is collected into a spherical, or ovoid, or pear-shaped mass. In others, again, irregular grains stained blue are scattered throughout the central portion.

2. From a section of a portion of the growth removed from a boy during life. The tissue was hardened in alcohol, and cut in celloidin. The section was stained with Gram's method and orange-rubin. There are several rosettes, surrounded by granulation tissue.

3. A mass of extremely fine filaments occupies the central part of the rosette. Many of the filaments have a terminal enlargement. The marginal part shows a palisade of clubs stained by the orange-rubin. x 500.

BACTERIOLOGY.

INTRODUCTION.

THE GERM THEORY.

THE researches of Pasteur into the role played by micro-organisms in the processes of fermentation and putrefaction, and in diseases such as anthrax, the silkworm malady, pyæmia, septicæmia, and chicken cholera, have invested the science of Bacteriology with universal interest and vast importance. The further researches of the practical mind of Lister, with the resulting evolution of antiseptic surgery, have demonstrated the necessity for a more intimate acquaintance with the lifehistory of these micro-organisms; while the more recent investigations which have established the intimate connection between bacteria and infective diseases, and more especially the discovery by Koch of the tubercle and cholera bacilli, have claimed the attention of the whole thinking world.

Those bacteria which are connected with disease, and more especially those which have been proved

to be the causa, if not the actual materies morbi, are of predominant interest and importance.

The first attempt to demonstrate the germ theory of disease dates back almost to the discovery of the microscope. Athanasius Kircher, nearly two and a half centuries ago, expressed his belief that there were definite micro-organisms to which diseases were attributable. The microscope had revealed that all decomposing substances swarmed with countless micro-organisms which were invisible to the naked eye, and Kircher sought for similar organisms in diseases which he considered might be due to their agency. The microscope which he described obviously could not admit of the possibility of studying, or even detecting, the microorganisms which are now known to be associated with certain diseases; and it is not surprising that his teachings did not at the time gain much attention. They were destined, however, to receive a great impetus from the discoveries which emanated from "the father of microscopy."

Antony van Leeuwenhoek had learned as a youth to grind and polish lenses, and later in life employed his spare time in constructing microscopes, and in conducting those researches which have made for him a name which is familiar to all microscopists. His researches were published in a series of letters to the Royal Society. In 1675 he described extremely minute organisms in * Ars Magna Lucis et Umbræ, 1646.

rain-water, well-water, infusions of pepper, hay, and other vegetable and animal substances, in saliva, and in scrapings from the teeth; and, further, he was able to differentiate these minute living things by their size, their form, and the character of their movements. In 1683 these discoveries were illustrated by means of woodcuts, and there can be little doubt, from the drawings of these microorganisms, that they are intended to represent leptothrix filaments, vibrios, and spirilla. Indeed, we can almost recognise these micro-organisms as bacteria from Leeuwenhoek's graphic descriptions, apart from his figures. They were described as moving in the most characteristic manner, progressing with great rapidity, or spinning round like a top, and as so excessively minute that they were only perceived with great difficulty. The smallest forms could hardly be examined individually; but, viewed en masse, they closely resembled a swarm of gnats or flies. In another communication, published in 1692, he gives some idea of the size of these animalcules by stating that they were a thousand times smaller than a grain of sand. Others which, comparatively speaking, were of considerable length, were characterised by their peculiar mode of progression, bending and rolling on themselves, movements which, he adds, created both delight and astonishment in the mind of the observer. Leeuwenhoek himself was not disposed to believe in the possibility of such organisms