646 



NA TURE 



[Oct. 30, 1! 



mined to discover the ratio of thickness between the body of the 

 Bacterium and its flagellant — that is to say, to discover how many 

 of the flagella laid side by side would make up the width of the 

 body. 



I proceeded thus. This is a complicated microscope placed 

 on a tripod, so arranged that it may be conveniently worked 

 upright. There is a special instrument for centering and illuminat- 

 ing. On the stage of the instrument, the Bacterium with its 

 flagellum in distinct focus is placed. Instead of the simple eye- 

 piece a camera lucida is placed upon it. This instrument is so 

 constructed that it appears to throw the image of the object upon 

 the white sheet of paper on the small table at the right hand 

 where the drawing is made, at the same time that it enables 

 the same eye to see the pencil and the right hand. In this 

 way I made a careful drawing of B. termo and its flagellum, 

 magnified 5000 diameters. Here is a projection of the drawing 

 made. But I subsequently avoided paper, and used under the 

 camera a most carefully prepared surface of ground glass. When 

 the drawing was made I placed on the drawing a drop of 

 Canada balsam, and covered it with a circle of thin glass, 

 just like any other microscopic mounted object. This is a 

 micro-slide so prepared. Now you can see that I only have to lay 

 this on the stage of a microscope, make it an object for a low 

 power, and use a screw micrometer to find how many flagella go 

 to the making of a body. The result is given in the figure : yuu 

 see that ten flagella would fill the area occupied by the diameter 

 of the body. 



In the cive chosen the body was the i/2O4O0th of an inch wide, 

 and therefore, when divided by ten, gave for the flagellum a 

 thickness of the i/2O4O0oth of an English inch. In the end I 

 made fifty separate drawings with four separate lenses. I 

 averaged the result in each fifty ; and then took the average of 

 the total of 200, and the mean value of the width of the 

 flagellum was the 1/2047001)1 of an English inch. It will be 

 seen, then, that we are possessed of instruments winch, when 

 competently used, will enable us to study the life-histories of the 

 putrefactive organisms, although they are the minutest forms 

 ot life. 1 have stated that they were the inevitable accompani- 

 ments of putrescence and decay. You learned from a previous 

 illustration the general appearance of the Bacteria : they are the 

 earliesl to appear whenever putrefaction shows itself. In fact, 

 the pioneer is this — the ubiquitous Bacterium termo. The order 

 of succession of the other forms is by no means certain. But 

 whenever a high stage of dec imposition is reached a group of 

 forms represented by these three will swarm the fluid. 

 These are the Monads, they are strictly putrefactive oi 

 they are midway in sue between the least and largest Bacteria, 

 and are, from their form and other conditions, more amenable to 

 research, and twelve years ago I resolved, with the highest power 

 lenses and considerable practice in their use, to attick the 

 pro >le 1 of their origin ; whether as physical products of the not- 

 livimj, or as the naturd progeny of parents. 



But you will remember that only a minute drop of fluid con- 

 11 can be examined at one time. This minute drop has 

 : ed with a minute film of glass not more than the 200th 

 of an inch thick. The highest lenses are employed, working so 

 near as almost to touch the delicate cover. Clearly, then, the 

 film of fluid would rapidly evaporate and cause the destruction of 

 the object studied. To prevent this an arrangement was devised 

 by which the lens and the covered fluid under examination were 

 used in an air-tight chamber, the air of which was kept in a 

 saturated condition ; so that being like a saturated sponge unable 

 to take in any more it left the film of fluid unaffected. But to 

 make the work efficient I soon found that there must be a second 

 Observation by leaps was of no avail. To be 

 accurate it must be unbroken. There must be no gap in a 

 chain of demonstration. A thousand mishaps would occur in 

 trying to follow a single organism through all the changes of 

 hours to the end. But, however many failures, it 

 was evident we must begin on another form at the earliest point 

 again, and follow it to the close. I saw soon that every other 

 method _ would have been merely empirical, a mere piecemeal 

 of imagination and fact. When one observer's ability to continue 

 a long observation was exhausted, there must be another at hand 

 to take up the thread and continue it ; and thus to the end. I 

 was fortunate indeed at this time in securing the ready and en- 

 thusiastic aid of Dr. J. J. Drysdale, of Liverpool, who practi- 

 cally lived with me for the purpose and went side by side with 

 me to the work. We admitted nothing which we had not both 

 seen, and we succeeded each other consecutively, whenever 



needful, in following to the end the complete life-histories of six 

 of these remarkable forms. 



I will now give you the facts in relation to two which shall 

 be typical. We obtained them in enormous abundance in a 

 maceration of fish. I will not take them in the order of our 

 researches, but shall find it best to examine the largest and 

 the smallest. The appearance of the former is now before 

 you. It is divergent from the common type when seen in 

 its perfect condition, avoiding the oval form, but it resumes it in 

 metamorphosis. It is comparatively huge in its proportions, its 

 average extreme length being the I, oooth of an inch. Its 

 normal form is rigidly adhered to as that of a rotifer or a crusta- 

 cean. Its body-substance is a structureless sarcode. Its differ- 

 entiations are a nucleus-like body, not common to the monads ; 

 generally a pair of dilating vacuoles, which open and close like the 

 human eyelid, ten to twenty times in every minute ; and lastly, 

 the unusual number of four flagella. That the power of motion 

 in these forms and in the Bacteria is dependent upon these 

 flagella I believe there can be no reasonable doubt. In the 

 monads, the versatility, rapidity, and power of movement are 

 always correlated with the number of these. The one before 

 us could sweep across the field with majestic slowness, or dart 

 with lightning swiftness and a swallow's grace. It could gyrate 

 in a spiral, or spin on its axis in a rectilinear path like a rifled 

 bullet. It could dart up or down, and begin, arrest, or change 

 its motion with a grace and power which at once astonish and 

 entrance. Fixing on one of these monads then, we followed it 

 doggedly by a never ceasing movement of a "mechanical stage," 

 never for an instant losing it through all its wanderings and 

 gyrations. We found that in the course of minutes, or of hours, 

 the sharpness of its outline slowly vanish, its vacuoles disappear, 

 and it lost its sharp caudal extremity, and was sluggishly 

 amoeboid. This condition intensified, the amoeboid action 

 quickened as here depicted, the agility of motion ceased, 

 the nucleus body became strongly developed, and the whole 

 sarcode was in a state of vivid and glittering action. 



If now it be sharply and specially looked for it will be seen 

 that the root of the flagella splits, dividing henceforth into two 

 separate pairs. At the same moment a motion is set up which 

 pulls the divided pairs asunder, making the interval of sarcode 

 to grow constantly greater between them. During this time 

 the nuclear body has c mmenced and continued a process of 

 self-divi ion ; from this moment the organism grows rapidly 

 rounder, the flagella swiftly diverge. A beau-like form is 

 taken; the nucleus divides, and a constriction is suddenly 

 devel ped ; this deepens ; the opposite position of the flagella 

 ensues, the nearly divided forms now vigorously pull in 

 opposite directions, the constriction is thus deepened a id the 

 tail formed. The fibre of sarcode, to which the constricted 

 part has by tension been reduced, now snaps, and two organ- 

 isms go free. It will have struck you that the new organism 

 enters upon its career with only two flagella and the normal organ- 

 ism is possessed of four. But in a few uiinutes, three or four 

 at mjst, the full complement were always there. How they 

 were acquired it was the work of months to discover, but at 

 last the mystery w is solved. The newly-fissioned form darted 

 irregularly and rapidly for a brief space, then fixed itself to the 

 floor or to a rigid object by ihe ends of its flagella, and, 

 with its body moti mless, an intense vibratory action was set up 

 along the entire length of these exquisite fibres. Rapidly the 

 ends split, <-ne half t-eing in each fibre set free, and the other 

 remaining fixed, and in 130 seconds each entire flagellum was 

 divided into a perfec pair. 



Now the amoeboid state is a notable phenomenon throughout 

 the monads as preclusive of striking change. It appears to 

 subserve the purpose of the more facile acquisition and digestion 

 of food at a crisis. And this augmented the difficulty of dis- 

 covering further change ; and only persistent effort enabled us 

 to discover that with comparative rareness there appeared 

 a form in an amoeboid state that was unique. It was a con- 

 dition chiefly confined to the caudal end, the sarcode having 

 become diffluent, hyaline, and intensely rapid in the protrusion 

 and retraction of its substance, while the nuclear body becomes 

 enormously enlarged. These never appear alone ; forms in a 

 like condition are diffused throughout the fluid, and may swim 

 in this state for hours. Meanwhile, the diffluence causes a 

 spreading and flattening of the sarcode, and swimming gives 

 place to creeping, while the flagella violently lash. In this con- 

 dition two forms meet by apparent accident, the protrusions 

 touch, and instant fusion supervenes. In the course of a few 



