spirostomum ambiguum 39b 



2. Material and Methods. 



The Spirostoiiia from which the cultures were started were 

 ohtcimed from ponds in North Cheshire, principally in the 

 neighbourhood of Ringway and Styal near Manchester. They 

 were most numerous in rather deep ponds, with muddy bottoms 

 covered with decaying vegetable matter, and with Lemna 

 covering the surface. A good supply was obtained during 

 the drought of the summer of 1921 whilst the ponds were low 

 and the water fairly concentrated, but all through the autumn 

 and winter, though a large number of ponds were visited, 

 including those visited in the summer, very few specimens were 

 obtained. In May and June they became plentiful again 

 and obviously were multiplying rapidly, since many dividing 

 forms were collected. 



Fixation . — The fixation of S p i r o s t o m u m a m b i g u u m 

 is very unsatisfactory because the animal possesses very highly 

 developed powers of contraction. Attempts to narcotize 

 them with chloroform, ether, carbon-dioxide, or by the action 

 of Epsom salts proved unsuccessful, though the narcotics were 

 used in minute quantities and in very dilute solutions. 



Bouin's solution and hot or cold Schaudinn's solution are 

 both good fixatives for the nuclear structures. For whole 

 mounts hot Schaudinn's solution gives the best results, since 

 the contraction of the cell is less with this fixative. When 

 whole mounts were required, the animals, together with as 

 small a quantity of culture fluid as was possible, were placed 

 on a slide smeared with egg albumen. The hot Schaudinn's 

 solution was dropped rapidly on the animals whilst they were 

 extended. Contraction of the whole body invariably took 

 place, but by this method there was no shrinkage of the 

 endoplasm from the ectoplasm. This contraction of the body 

 was not really very disastrous, since the main outline of the 

 meganucleus and its relative position were easily studied in the 

 living animal and fixed i3reparations were required for detailed 

 study. 



It was found best, whenever possible, to starve the material 



