28 
Proceedings of the Royal Society of Edinburgh. [Sess. 
is not always, nor even normally, the case. Also no spiral twisting is 
observable, neither is the edge of the individual thicker than the middle 
portion. I invariably found this organism motile at this stage. The 
motility consists of a wriggly movement, accompanied by a slow, pendulum 
movement, as if one end had one or more cilia attached. I have not, as 
yet, been able to demonstrate the organs of motion. The next stage in 
the development of the cell is seen in fig. 14. The thinner terminal portion 
was partly twisted, and in fig. 15 a complete twist has been accomplished. 
The young cell is still grey and transparent, has no thickened edge, and 
no deposit of iron. The length is about 14 ju, and the breadth varies from 
1J /ul in the widest to 1 jm in the narrowest portion. A still further 
stage is shown in fig. 16, in which two turns have been accomplished. 
In this individual no change had taken place except for this extra spiral 
turn; it moved about very slowly in a forward direction, exhibiting in 
addition a trembling movement. Later stages are shown in figs. 10, 18, 
19. In the individual represented by fig. 18 there was no deposit, but in 
those shown in figs. 9, 19 a slight deposit had begun to be formed, as 
shown by the loss of its grey, semi-transparent character and its assumption 
of a pale, brownish-red colour. Movement had stopped, and during the 
rest of the life-history of the individual, is not again assumed. The 
deposition of iron, the formation of conidia, and the thickening of the 
edges are inimical to movement. From this point on, growth in length 
and width had evidently taken place, and conidia were rapidly formed. 
All stages and all sizes were observed, the twisting with the variations in 
the length, width, and twist-length causing a large variety of forms, 
which, if one had not seen the intermediate stages, would incline one to 
believe that we were dealing with several species. 
The Cultuee of Spieophyllum feeeugineum. 
I have made numerous experiments with the object of cultivating this 
form, and have tried most of the methods tried by others in their efforts 
to obtain pure cultures of other iron-bacteria. Winogradsky gives one 
method which was not at all successful with this form, nor indeed was 
it with Leptothrix and Gallionella. 
The methods found to be successful by others, resulted, in my cultures, 
in a preponderance of an undesired bacillus or coccus and a consequent 
extinction of the desired organism. This must often be the case in 
bacteriological experiments, for the preponderance of any one form depends 
on the sum total of conditions being favourable to it, and the sum total 
is never the same in any two localities. It is not necessary to state all 
