1878.] the Life-History of a Minute Septic Organism, 333 



not until the latter part of the summer of 1876 that I found it again. 

 It appeared then, in a maceration, in which the body of a vole was 

 decomposing. The maceration was only three weeks old, and this 

 organism had evidently only just arisen ; it increased daily in vigour 

 and numbers, and in three weeks I was at liberty to study it con- 

 tinuously. 



For this purpose I employed the " continuous stage," jointly 

 devised for preceding researches,* by means of which a drop of the 

 infusion could be kept under examination, without evaporation, for an 

 indefinite time, and with the most powerful lenses. f 



My method was to follow out, as far as possible, the morphological 

 details separately ;. and then to steadily follow one form from its 

 earliest to its most mature condition; thus discovering how the 

 different states were related, and making out an unbroken life-history. 



Most of the more difficult and delicate work was done with an 

 entirely new lens, made specially for me by Messrs. Powell and 

 Lealand ; and which is nominally a -^th. inch lens. It was made spe- 

 cially for this class of investigation, for which it is admirably adapted. 

 Its "working distance" is sufficient; its "penetration," for such a 

 power, is extremely great, its angle being moderate ; and its " defini- 

 tion " is as sharp and clear, when properly used, as that of the finest 

 ^th or -|th. I also had the advantage of the use of the four new 

 lenses made on a "new formula " by the same makers, viz., a -|-th of 

 low angle and great penetrating power ; and a -i-th, T Vth, and T Vth of 

 high angles. I also used the ^th and y^th lenses. 



One of the difficulties attending the study of this organism was its 

 extreme rapidity and caprice of movement. Its normal form is 

 depicted at fig. 1, Plate 8. It is there magnified 3,000 diameters. 

 Its sarcode is clear, and to all the lenses employed structureless. It is 

 usually found to have minute vacuoles scattered through it. The 

 form of the body is distinctive. Its greater part is a long oval 

 slightly constricted a little above the middle. But from the front, or 

 shorter portion, a kind of neck (a, fig. 1) protrudes, from which pro- 

 ceeds the front flagellum, which is extremely fine, and from one and 

 a-half times to twice as long as the body. Below this and at the 

 sides or "shoulders" of the organism, two other long and fine flagella 

 arise, proceeding backwards, as seen at b, c, ibid. In addition to this, 

 there is always a nucleus-like body slightly to one side of the lower 

 part of the organism, as seen at d ; and with the higher lenses and 

 delicate manipulation there was frequently seen, within this, an ex- 



* Vide "Further Researches into the Life-History of the Monads." Monthly 

 Micro. Journal, vol. xi, pp. 97-99. 



f Linen instead of bibulous paper is now used as the agent for conveying a con- 

 stant supply of evaporating moisture to the chamber in which the organisms are 

 examined in this piece of apparatus. 



z2 



