Schönwerth ( Ueber die Möglichkeit einer von Brunnenwasser ausgehenden Hühnercholera-Epizootie,' Archiv f. Hygiene, vol. xv. 1892, pp. 60-106) has investigated the virulence of the B. cholera gallinarum (p. 324) in water by infecting certain wells, the temperature of which was 6.5°-7.9° C., with broth-cultures of the organism, and subsequently using it in feeding fowls and pigeons. Although these animals were fed for 16-20 days with this water, none of them developed any symptoms of chicken cholera. The same results were obtained in two distinct series of investigations. In another experiment the conditions were slightly varied, the infected water being rendered just alkaline with soda before being given to one of the fowls. This bird died in fourteen days of typical fowl-cholera. In another investigation, instead of infecting the well-water with broth-cultures, the bacilli were introduced without adding any culture material, but the same negative results were obtained. In another experiment the water was infected with the blood and juices of organs of birds which had died of chicken-cholera, but no pathogenic effect resulted. In order to test the actual virulence of the water some of the birds were inoculated with increasing doses (1-8 c.c.) of the water in each case; it was in this manner ascertained, judging by the length of time which elapsed between the infection and death of the bird, that in one case the virulence of the water infected with broth-cultures lasted 540 hours, in another 260 hours, whilst in the water infected with bacilli without broth, and in which a larger number were introduced, the virulence disappeared in 144 hours. In the case of the water into which the blood and juices. of infected birds were introduced the virulence only disappeared after 220 hours, in spite of a much smaller number being employed. The author is of opinion,

therefore, that the bacilli introduced directly from the body of an animal are more vigorous and virulent than those taken from cultures; also that the simultaneous introduction of culture material with the bacilli serves to prolong the virulence of the latter.

The experiments on the behaviour of the sporiferous tetanus bacillus are amongst the most interesting which have been made in connection with the vitality of pathogenic bacteria in water. In some respects the results resemble those obtained by one of us on anthrax spores -thus, in the practically indefinite virulence in sterile waters, and the degeneration in unsterile ones. Altogether unique, however, is the recrudescence of the virulence exhibited by the tetanus bacilli, which is an observation of such fundamental importance as to demand further investigation.

Schwarz explains this attenuation of the tetanus organisms in the unsterilised waters as a consequence of the multiplication of the ordinary water bacteria present. He examined by means of plate culture the behaviour of the latter, and found that from the day of the introduction of the tetanus bacilli until the period when the attenuation of the latter was observed these water forms multiplied steadily, until the point. was reached to which we have so often referred when their numbers again began to diminish. Schwarz throws out the suggestion that the attenuation of the tetanus organism may not only be due to the extensive. multiplication of the water bacteria, stimulated by the culture-material which was introduced when the waters were first infected with tetanus, but may also depend upon the particular varieties of water microbes present; and that the recovery of their virulence by the former may be due to the subordination of the latter when their diminution became marked.

In order to show that this attenuation of the tetanus virus in unsterilised waters is due to the presence of other bacteria, Schwarz inoculated sterilised sea-water, not with a pure culture of tetanus, but, on the contrary, with an impure though virulent cultivation. Instead of the tetanus remaining for an indefinite length of time in a virulent condition, as had previously been observed in the case of sterilised sea-water, it was found to have become on the twentieth day already so attenuated, that on inoculating animals in the usual manner with some of the water their death only took place after a lapse of twenty-one days from the date of inoculation, and unaccompanied by any typical tetanic symptoms excepting extreme emaciation.

It will be seen from a careful study of the numerous investigations which have been made on the behaviour of pathogenic organisms in water what enormous differences exist in their capacity for living in this medium; that whereas some varieties are destroyed in a few hours, some will live and flourish for many months. Moreover, it is obvious how greatly in some cases the character of the water influences the vitality of the micro-organisms, a point which is especially brought out in Trenkmann's experiments on the cholera bacillus ; and it is of particular interest to note how in the case of unsterilised waters the ordinary water bacteria are able to overwhelm and suppress those foreign pathogenic forms which have been introduced. Kraus's experiments are particularly instructive in this respect, for they exhibit the multiplication which takes place in the ordinary water bacteria, and the simultaneous. disappearance which ensues of the pathogenic organisms introduced. The experiments on anthrax demonstrate conclusively the immensely greater vital powers possessed by the spore over the bacillar form

when introduced into water, and the necessity of differentiating between these two forms in carrying out such researches. Moreover, it cannot be too rigidly insisted upon that every precaution must be taken to avoid the introduction with the organism of any appreciable quantity of culture-material into the experimental waters. It is apparent how entirely the character of the water may be modified by a neglect of this precaution, and that a water originally incapable of supporting a pathogenic organism in question may be transformed into a suitable medium in which it will not only live but multiply. Unfortunately, many investigators have ignored this possibility, and hence we sometimes find such conflicting information recorded of the behaviour of one and the same organism in water.

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CHAPTER IX.

THE ACTION OF LIGHT ON MICRO-ORGANISMS IN WATER AND CULTURE MEDIA

THE above subject, although at first sight somewhat outside the application of bacteriological science which we have so far been considering, is one of such immense importance in connection with the vital phenomena of bacteria, and is indissolubly associated with so many of the problems with which the investigator is confronted, that a knowledge of what has been already achieved in this direction is essential to those who purpose taking up the study of micro-organisms in water. Indeed, some of the more recent experiments have a direct bearing upon the questions we have been discussing, and whilst, therefore, giving a general survey of the researches on light which have so far been made, a more particular account will be found of those investigations which are concerned with the behaviour of micro-organisms in water when exposed to light.

To Downes and Blunt belongs the credit, not only of having first demonstrated the bactericidal effect of light in a memoir published in the Proceedings of the Royal Society in 1877, but in having at once so perfectly indicated almost all the factors connected with this action that the further investigations which have been carried out on this subject during the past fifteen years

1 Researches on the Effect of Light upon Bacteria and other Organisms,' Proc. Roy. Soc. vol. xxvi. No. 184, 1877, Dec. 6.