s^ 



NATURE 



[May 25, 1S93 



degree, and when the spectrum of such a solution is examined it 

 is seen to present a characteristic absorption-band in green ; 

 the spectrum of a watery distribution of these bacteria shows 

 two bands : one narrow one in green, the other broader in 

 greenish-blue ; both are less deep than the single band of the 

 alcoholic solution. 



Nor have I sufficient time to do more than allude to another 

 remarkable group of bacteria, which comprises several species, 

 all having the power to produce luminosity of themselves and 

 the medium in which they grow. These phosphorescent bacteria 

 have been long known (Pfliiger) to be concerned in the produc- 

 tion of the phosphorescent condition of decomposing sea fish, but 

 within recent times Ludwig, Fischer, Katz, and particularly 

 Beyerinck have studied more in detail the conditions under which 

 these bacteria grow, and have identified and cultivated several 

 species. Dr. Beyerinck has kindly sent me one species 

 of these phosphorescent bacteria. The elements of this species 

 are short oval rods, often dumb-bells ; they grow in fish broth, 

 and when the growth becomes conspicuous to the unaided eye 

 it is luminous when viewed in the dark. I show you here some 

 cultures which, as you see, when I place them in the dark, show a 

 beautiful phosphorescent appearance. The phosphorescence is 

 more or less limited to the surface layer, that is the one in con- 

 tact with the oxygen of the air ; in the depth it is absent, but 

 when shaking the flask the phosphorescence appears also in the 

 depth. 



Fermentation. 

 I have mentioned, in connection with a previous group, 

 bacterial species which have the power to change by 

 hydration urea into ammonium carbonate, a change which is 

 called a fermentative action. Changes similar to these are 

 caused by micro-organisms in many processes playing an im- 

 portant part in industries. Amongst these changes I may 

 mention one in particular, the souring of milk. There are a 

 good many others, the viscous or mannit fermentation, the 

 butyric fermentation, the indigo fermentation, the dextran fer- 

 mentation, the acetic acid fermentation, and others, but time does 

 not permit me to describe more than one, viz. the common 

 bacterium lactis. I show you here a number of photographs of 

 the bacterium lactis under cultivation, and as seen under the 

 microscope. It is a minute oval bacterium, which multiplies 

 with great rapidity, and which, introduced into milk, turns this 

 sour in 12 to 24 hours at the ordinary temperature ; when sterile 

 milk is inoculated with this bacterium and kept in a warm place 

 at a temperature of 60° to 65" !•'., the milk is found solid and 

 curdled before 20 or 24 hours are over, and in this curdled milk 

 large numbers of the bacterium lactis are present either as dumb- 

 bell ovals or as short chains. When a needle is dipped first into 

 such curdled milk and then into normal milk, the same coagu- 

 lation with the same appearances takes place in the latter. 

 When a plate cultivation of such milk is made it is seen that 

 a large number of colonies all of the same character are 

 developed, which colonies are made up of the bacterium lactis ; 

 through however numerous generations this organism is 

 cultivated in artificial cultivations, — it grows well on 

 nutritive gelatine to which whey or only lactic sugar 

 has been added — and if then transferred to fresh milk, it always 

 produces this souring and curdling ; that is to say, it changes 

 lactic sugar into lactic acid, and as this is being formed it coagu- 

 lates and precipitates the casein of the milk. With a trace of 

 milk that has gone naturally sour — that is to say, to which the 

 bacterium lactis has found entrance, and in which by its multi- 

 plication it has produced curdling, any amount of normal milk 

 can be successively turned sour and curdled. The bacterium 

 lactis is not by any means a rare organism ; it is widely dis- 

 tributed, and can at any moment, in dairies and other places, 

 through impurities of the utensils, by dust, &c., find access to 

 milk which would soon succumb to its attacks ; when, for 

 instance, in dairies or in one or another locality the milk has a 

 frequent tendency to turn sour, this means that the bac- 

 terium lactis has taken firm footing in such a locality. It is 

 well known that only extreme measures of cleanliness, thorough 

 boiling of all utensils and vessels, cleaning of walls and floors 

 can banish or reduce it. In this the analogy with an epi- 

 demic of an infectious disease is obvious. Just as in an epidemic, 

 every susceptible individual to which the contagion has had 

 access becomes smitten by infection, and just as in an epidemic 

 the contagium of the disease, being of wide distribution, and, 

 having taken a firm hold of the locality, attacks an increasing 

 number of individuals, and thus causes the epidemic— so also 



NO. 1230, VOL. 48] 



in the case of the bacterium lactis : when this has taken a firm 

 hold of, and has acquired a great distribution in, any locality, 

 any sample of milk (i.e. susceptible individual) may take the 

 infection, either by coming in contact, directly or indirectly, 

 with a trace of the milk already infected, e.g. by being placed 

 in vessels in which infected milk has been kept previously, or 

 becoming infected through dust charged with the bacterium 

 lactis, or coming in contact with water poured from a vessel in 

 which traces of the microbes were still left. All this finds its 

 complete analogy in the case of an epidemic infectious disease. 

 The fermentative processes due to microbic activity, and playing 

 an important part in industries (alcoholic and other fermenta- 

 tions), illustrate in a very striking manner some of the essential 

 features observed in the nature, in the production, and in the 

 spread of infectious diseases in man and animals. The fermen- 

 tative processes, thoroughly established as being due to microbic 

 activity by the researches of Pasteur, were by Pasteur, and 

 others alter him, used as illustrations of the way in 

 which infectious disorders in man and animals arise, and it 

 \yas exactly these considerations which led Pasteur to his bril- 

 liant studies of these diseases, the results of which studies 

 have been of such signal service insanitary science in general, 

 and in the prevention of infectious diseases in particular. 



In the fermentative processes studied by Pasteur and others 

 it was shown that each specific fermentative process is due to 

 the growth and multiplication of a specific microbe. Just the 

 same is the case with the infectious diseases — when from a 

 substance which is in the process of fermentation, a trace con- 

 taining the particular microbe is introduced into fresh fermentible 

 substance, this latter undergoes the same fermentation ; further, 

 it is shown that, however great the number of accidental non- 

 specificbacteria which may be introduced at the same time, unless 

 that particular bacterium be present amongst them, the specific 

 fermentative change does not ensue. The same is the case with 

 infectious diseases : the number of non-specificbacteria in water, 

 dust, air, various common articles of food, &c,, is sometimes 

 great, but no amount of these would set up any of the infectious 

 diseases, like cholera or typhoid fever, tetanus or diphtheria ; 

 in order to do so there must be amongst them the particular 

 microbe of cholera or typhoid fever, &c. Again, in each fer- 

 mentative process the substance which is to undergo thefn- 

 mentation must be susceptible of the particular fermentation : a 

 substance that contains sugar can undergo the alcoholic fermen- 

 tation, a substance that contains alcohol cr.n undergo the acetic 

 acid fermentation, &c. The same is the case in the infectiou-i 

 diseases : an individual must be susceptible to the disease, though 

 it is not quite clearly established what the meaning of this is. 

 Further : just as in the fermentative process the susceptibility of 

 the substance alone is not sufficient, is only a preliminary con- 

 dition, the actual infection with the specific microbe being the 

 essential, so also in the infectious disease : in order that a sus- 

 ceptible individual should become the subject of the disease it is 

 essential that the specific microbe should be present and should 

 find entrance into this susceptible individual. Just as little as a 

 particular condition of the atmosphere, of temperature, &c., is 

 capable of producing the souring of milk, so also a particular 

 atmospheric or telluric condition, season, or other external cir- 

 cumstances alone cannot produce an infectious disease. What 

 is wanted in the first place is the presence of the bacterium lactis 

 in the one, the specific pathogenic microbe in the other ; at- 

 mospheric or telluric conditions may and do favour the more 

 rapid multiplication and dissemination of the bacterium lactis or 

 other specific microbes, but without the presence of the specific 

 microbes these processes could not take place. "Thunder in 

 the air " could not turn the milk sour, could not make meat 

 tainted, could not turn beer or wine sour, without the presence 

 of the specific microbes, which by their presence and multipli- 

 cation produce those undesired changes in these substances ; the 

 particular condition of the air could and would increase their 

 rate of multiplication and distribution, and therefore increase the 

 chances of infection of these substances and therefore a more 

 conspicuous manifestation of the effects of the activity of those 

 microbes, but it could not produce the microbes themselves. ^ ; 



Pathogenic Bacteria. 



The different pathogenic bacteria connected with and causing 

 the difi'erent infectious diseases have then the power of growini; 

 and multiplying within the infected individual and through the 

 different poisonous substances^toxins — which they therein 



