,')70 K. M. NKLSON ON SoMK MINUTK KOK'MS OK I'OND lAVi:. 



Leaving now inikiiowii ground, wc come to an organism which 

 can be recognized as a Spirocha'ta plicatilis. 



It was not a large specimen, being in length about a 

 thousandth of an inch, and as thick as a tubercle bacillus. 



The mov^ement of this organism was so peculiar and interest- 

 ing that it is worth describing at some length. 



If a spiral is wound round a journal revolving in bearings its 

 motion will not appear as a rotation, but as a progression in a 

 line with the axis of the journal. This optical illusion is some- 

 times employed for the j)urposc of imitating a cascade of water 

 by means of rotating ghiss spirals. But if the journal be ad- 

 vanced during every revolution a distance equal to the pitch of 

 the screw, then ilie spiral will appear to be perfectly stationary. 



The form of the ordinary Spirocha3ta is well known ; 

 among the various wriggling and other movements of this 

 organism one is especially important. Suppose we adjust and 

 focus an oil j\ giving 1,500 diameters on one particular con- 

 volution in the middle of the organism, we shall see that while 

 this particular convolution is apparently stationary the end on 

 one side is being rapidly drawn in towards the middle, while 

 the other end is as rapidly extended. This movement is then 

 repeated in a contrary direction, and often several times back- 

 wards and forwards in succession. At first I was com])letely 

 deceived by this complicated movement, and was eagerly 

 seeking for some swelling or thickening of the body, which 

 would permit of a contraction at one end and a corresponding 

 thinning of the other side to allow of an extension. 



After being engaged in this fruitless search for some con- 

 siderable time I at length perceived the true explanation, viz., 

 that the spiral rotated at a high velocity, the organism ad- 

 vancing a distance equal to the pitch of the screw during each 

 revolution. 



It is interesting to note the marked difference between the 

 appearance of this organism and a Spirillum. A spirillum does 

 not advance nearly so much as the length of the pitch of the 

 screw during each revolution, consequently it appears when in 

 movement like a hollow ellipsoid made of spirally interlacing 

 bands of basket-work, an effect wholly different to that pro- 

 duced by a moving Spirochfeta. 



