as other organisms are often also present, but there is generally no difficulty in obtaining a pure culture. The explanation of the ease with which a culture can be obtained is that the mouth streptococcus grows with great rapidity in almost all media, to the exclusion of other organisms.

The streptococcus obtained from various mouths often differ slightly in their cultural characters, but in their general behaviour they conform to the type of von Lingelsheim's1 Streptococcus brevis, as noted by Dr. Washbourn and myself.2 Since that paper was published I have obtained the streptococci from 150 consecutive mouths examined; all the cultures obtained conformed to the general characters given below. All of them produced an acid reaction when grown in carbohydrate media (broth to which 2 per cent. of lactose, maltose, glucose, dextrin, cane sugar, or starch had been added). The starch and cane sugar media require the longest to develop the acid reaction, whilst in the other solutions the reaction is often strongly acid in six hours.

The streptococci also clot milk into a solid mass in forty-eight hours.

In the paper quoted above it was noted in connection with the mouth streptococcus that among other characters the few inoculation experiments performed confirmed von Lingelsheim's view that the mouth streptococcus differed from the Streptococcus longus in not being pathogenic for guinea-pigs, rabbits and mice. Other observers are inclined to the view that the streptoccocus of the normal mouth is the ordinary pathogenic streptococcus which occurs in pyæmia and phlegmonous erysipelas. Pathogenic streptococci undoubtedly do occasionally occur in the normal mouth, as various observers have shown a fact that considerably complicates the problem. The pneumococcus occurs in normal human saliva in a distinctly pathogenic condition, so much so that a rabbit, an animal particularly susceptible to the pneumococcus, often dies subsequent to an inoculation with saliva, the pneumococcus being found in the blood after death. One of the races of pneumococci obtained from the saliva by Washbourn3 and Eyre were, however, apparently living in a saprophytic condition, and

1 Zeitschrift für Hygiene, Bd. x., p. 331.

2 Trans. Odont. Soc., June, 1896.

3 Brit. Med. Jour., Nov. 4, 1899.

their virulence was of low value until the organisms had been pssaed through the bodies of many animals; even then the pathogenicity of the species soon ran down when grown upon artificial media, whilst other races of pneumococci obtained from the rusty sputum of pneumonia retained their virulence for a considerable time. Virulent diphtheria bacilli may be present in normal mouths as well as other pathogenic organisms, and we may certainly also conclude that the streptococci of a pathogenic nature met with in the mouth from time to time are stray individuals of another species accidentally present, and not the common mouth inhabitant. This question of the identity of two presumably different organisms is a much wider question than the particular case of the mouth streptococcus; thus, for instance, B. coli communis and B. typhi abdominalis, B. diphtheria and the B. of Hoffmann, B. subtilis and B. anthracis, to mention only a few examples, are each related to the other in their cultural peculiarities, method of staining, &c., and somewhat minute differences are relied upon to differentiate the organism from its simulator. It is of course possible that the streptococcus of the mouth is a degenerate nonpathogenic and saprophytic variety of the Streptococcus longus, and that under some favourable conditions it may invade the tissues, as in severe scarlatinal angina, and produce serious results. On the other hand the mouth streptococcus may be a different species, having certain characters in common with the Streptococcus longus it is true, but differing from it in others, among which is its virulence. Lingelsheim1 was the first to point out that the streptococcus obtained from the normal mouth differed from the Streptococcus longus. Thus it was not pathogenic for rabbits or mice, it rendered broth uniformly turbid, and the chains on this medium were shorter than those of the Streptococcus longus and it caused a slight liquefaction of gelatin, and Lingelsheim therefore considered it a distinct species and named it the Streptococcus brevis, from the short chains formed on broth cultures. Marmorek, in opposition to this, looks upon all streptococci as simple varieties of the same species, which can all be raised to a uniform type by appropriate means, although various strains of streptococci obtained from different pathological conditions of the human subject behave differently when injected into animals.

:

In the paper already quoted the following conclusions are given "The streptococcus occurring in the normal mouth agrees with the S. brevis of Lingelsheim, and can be distinguished from the streptococcus of disease by its biological and morphological characters. It must be looked upon as a distinct species for the present, although ultimately this view may prove to be incorrect, for it is possible that further researches may enable us to convert the Streptococcus brevis into the Streptococcus longus. This, however, has not hitherto been accomplished. We think that the discrepancies of different observers who have investigated the question are partly due to the fact that the pathogenic Streptococcus longus is sometimes accidentally present and has been mistaken for the normal streptococcus of the mouth."

Subsequent research tends to confirm these conclusions, and for the present the S. brevis of the mouth is to be regarded as a distinct species and as the most constant of all mouth organisms. In perfectly clean and healthy mouths it is often the only organism met with.

Various other pathogenic organisms have been stated to be present in the normal mouth. Biondi particularly gives a list of five organisms of this class, which require notice. Of the five organisms in Biondi's list two were only met with once, in each case by inoculating an animal with saliva, the organism being found in the resulting abscess. These two organisms then (Coccus salivarius septicus and Staphylococcus salivarius pyogenes) can hardly be called true mouth bacteria.

The third on Biondi's list (Streptococcus septo-pyæmicus) is said to be indistinguishable from the streptococcus of pyæmia and erysipelas in its cultural peculiarities and its pathogenic action on animals, and there seems no reason to doubt that this streptococcus was the S. pyogenes which we have seen is at times present in the mouth.

The fourth organism described by Biondi is the Micrococcus tetragenous, whilst B. salivarius septicus has since been shown to be the same as the Diplococcus pneumoniæ.

1 Loc. cit.

2 Zeitschrift fur Hygiene, Bd. ii., 1887, p. 194.

(3) STAPHYLOCOCCUS AUREUS.

The Staphylococcus aureus, or golden coccus, first carefully described by Rosenbach in 1884, is commonly present in suppuration, abscesses (acute), boils, carbuncles, osteomyelitis, ostitis, &c., and occasionally in puerperal fever, infective endocarditis and pyæmia. In cultures from septic throats it is often present and is commonly found as a contamination in cultivations made from the throats of persons ill with diphtheria. Outside the body it may be found in air, soil, or water, but most frequently in dust, especially the dust of hospital wards.

The staphylococcus may occur in the eyes, ears, nose, mouth, and especially under the finger nails, whilst they are said to occur occasionally in the fæces of children.

I have several times obtained the staphylococcus aureus in pure cultivation from acute abscesses involving the roots of "dead teeth," but it is by no means always present, for in forty cases of oral suppuration around teeth they were only present three times, twice in pure culture. On two occasions I have found a pure culture of staphylococcus aureus in antral suppuration, but even in this region it is far from common.

In neglected and dirty mouths these organisms are occasionally to be found, in healthy mouths they are not often found.

The majority of observers agree that the S. aureus is by no means always present in the mouth, thus: Netter1 only found S. pyogenes aureus in seven out of 127 individuals examined; Vignal2 and Millers only found the pyogenic cocci occasionally; Black,' on the other hand found S. aureus in seven out of 10 cases examined. My own researches tend to confirm those of Netter and Miller, the S. aureus occurring in about 10 per cent. of all cases examined. On looking through the notes of the examination of 1,000 mouths, I find staphylococcus albus occurs eighty times, about 10 per cent. In these cases there was no special search made for the organisms, but the yellow colonies were observed in the ordinary process of cultivation, isolated and grown on the various test media.

A fact that may to some extent explain the rare occurrence of the staphylococcus aureus in the mouth is the bactericidal power of

the saliva experimentally proved by Sanarelli. Sanarelli1 filtered saliva through a Pasteur-Chamberland filter and tested the filtrate in the following way :

A small quantity of a pure cultivation of staphylococcus aureus, just as much as could be taken up on the point of a platinum needle, was added to 10 cubic centimetres of saliva sterilised by filtration. After mixing, plate cultivations were made, and the number of organisms present determined. Plate cultures were then made at intervals, and by this means it was found that the number of colonies developing gradually diminished, and in thirty-six hours no staphylococci were present.

If, however, a whole loopful of the cultivation was added, the plate cultivations still showed a diminution in the number of organisms present during the first two days, but after this the number again increased, until the colonies were uncountable.

It follows, therefore, that the saliva possesses a certain bactericidal power which is able to deal with small quantities, or isolated organisms, but that this power is quantitative, and that it is insufficient to deal with a large number. In this respect the action is similar to that of blood serum and other body fluids.

It is interesting to note that pneumococci were apparently not affected by the action of the saliva, and grew from the first.

Morphology.-Round, spherical or oval cocci, 0.6-0.9μ diameter, occurring in clusters or singly and in chains, showing a slight flattening at the point of mutual apposition. Not possessed of flagella. According to Du Bary and Hueppe arthrospores are formed; these consist of large swollen elements 1.0 to 1.5 μ wide, which stain deeply, other observers are inclined to regard such forms as degenerate cocci, and they are known also as involution forms." No endogenous spore formation is known to occur. Capsule not stainable.

Staining Reactions.-Retains the stain of Gram's method, and stains easily with the ordinary basic aniline dyes, carbol methylene blue, gentian violet, &c.

Biological Characters.-Non-motile, äerobic, facultative anäerobic, chromogenic coccus, with well marked fermentative and pathogenic powers.

Gelatin, 22° C.-Plates in forty-eight hours white punctate colonies, which rapidly liquefy the medium, microscopically granular, dark brown, entire.

1 Centr. für Bakteriol., Bd. x., 1891, p. 817.