ture of liquid air. The specimens of the consumption bacillus employed were originally obtained from the human subject, and they were exposed for periods varying from six hours to six weeks to 190° C. In each case the malignant properties of the tubercle bacillus after exposure were tested by their direct inoculation into animals, and the results compared with those which followed similar inoculations made with bacilli which had not been frozen in this manner, but had been grown in ordinary circumstances. In no single case, Mr. Swithinbank tells us, were these frozen tubercle bacilli deprived of their virulence, and the length of exposure, at any rate as far as could be judged after six weeks, appeared to make no difference in this respect. It is true that the pathogenic action of the frozen bacilli appeared to be somewhat retarded—that is, they took rather longer to kill animals than the ordinary unfrozen bacilli-but in every case their inoculation produced the typical tuberculous lesions associated with them.

Of particular interest, however, in view of what has been already discovered about the lethal effect upon bacteria of violent alternations of temperature, are Mr. Swithinbank's observations on the vitality of the tubercle bacillus when exposed to such extreme variations of temperature as are

represented by a passage from - 190° C. to that of 15° C.

The bacillus tuberculosis is admittedly a tough antagonist to deal with, and enjoys an unenviable notoriety for its robust constitution amongst the pathogenic members of the microbial world; hence a knowledge of its behaviour in these trying circumstances, as we now know them to be to bacterial life, becomes of special interest. Great must have been the investigator's satisfaction, then, when he discovered that the vitality of the consumption bacillus had been so seriously impaired by this treatment that its pathogenic properties collapsed, and the animals which were inoculated with these specimens, instead of with the continuously frozen bacilli, suffered no inconvenience, and remained in good health.

But although no appreciable change either in the structure, vitality, or malignant properties of the particular bacteria investigated have been noted as resulting from their exposure to extremely low temperatures, yet there is no doubt that a certain proportion of the individual micro-organisms present-those probably whose constitution is less robust than their more fortunate associates-do succumb under these trying conditions.

This fact has been well brought out by Dr. Belli, of the University of Padua, in the experi

ments which he made with the fowl-cholera bacillus and the anthrax bacillus in the presence of very low temperatures. Thus he exposed a large number of fowl-cholera bacilli in broth to the temperature of liquid air, as many as 396,000 bacilli being present in every twenty drops of the liquid. After exposing them continuously for nine hours to - 190° C., he had the curiosity, after thawing them, to count how many were left alive, and he found that an enormous mortality had taken place amongst them; for, instead of nearly 400,000 bacilli being present in one cubic centimetre, there were only about 9,000. On the other hand, in the broth tubes kept during that time in ordinary surroundings, the bacilli had flourished remarkably, and had greatly increased in numbers. Thus not only had no multiplication amongst these bacilli taken place, which circumstance is always regarded as indicative of their vital conditionnot only, then, had their vitality been arrested— but a very large number of them had been actually destroyed in consequence of this severe treatment; but that the residue were not only alive, but unimpaired in their energies on being restored to animation, was proved by their being able to destroy animals, not having parted with any of their malicious propensities. Dr. Belli carried out similar experiments with the bacilli of anthrax

and obtained very similar results.

With regard to both these varieties of pathogenic bacteria, he mentions that their action upon animals was not quite so rapid as is characteristic of normal specimens of these micro-organisms, thus confirming the experiments in this direction made with frozen. tubercle bacilli.

Not content with the exhibition of their powers of endurance, Dr. Belli determined to make yet another demand upon the vitality of these bacilli. For this purpose he immersed them in the liquid air itself, thus bringing them into direct contact with it, effecting this by lowering into the liquid strips of filter-paper soaked in broth containing these bacilli. But, in spite of remaining for the space of eight hours in these surroundings, they emerged triumphant, exhibiting no modification whatever either in their structure or pathogenic properties.

There are doubtless many other trials yet awaiting bacteria, to which they will most certainly be submitted before the limits of their powers of endurance have been adequately tested, but it is difficult to conceive of a severer strain upon their vital resources than the imposition of the conditions of which the above is but a brief sketch.

The triumphs achieved in this direction by micro-organisms are, however, closely approximated by the remarkable record established, according to

the recent researches of Dr. Krause, by typhoid, anthrax, tubercle, and some other bacteria of preserving unimpaired not only their vitality but their virulence after having undergone for a period of twenty hours a pressure of no less than that of 500 atmospheres. When we reflect that a pressure of 500 atmospheres is equal to a pressure of about 7,500 pounds to the square inch, and that the normal pressure under which life is maintained upon this planet is approximately that of fifteen pounds to the square inch, this bacterial victory over physical conditions will be more readily appreciated.

The more intimate becomes our knowledge of bacteria, the more must we marvel at the equipment with which they have been provided for enabling them to maintain themselves in the struggle for existence-a struggle which is as severe and as remorseless in this lowly region as it is in those domains the inhabitants of which have risen to far loftier heights on the great ladder of life.