BY R. GREIG-SMITH. 657 



disinfectants, appear to be little influenced by their own bacterio- 

 toxins, but are affected by the toxins of other bacteria. This indif- 

 ference was noted by Russell and Hutchinson, and altliough they 

 claim that no bacteriotoxins are present in soil, they speak of the 

 inhibiting action of bacteria added in tlie course of their experi- 

 mental work. 



These authors had tested the effect of the protozoa indirectly 

 by comparing the growth of bacteria in raw soils, or in treated 

 soils to which raw soil had been added, with the growth of bac- 

 teria contained in suspensions of raw soil freed from protozoa by 

 filtration through cotton wool. The effect of filtered and unfil- 

 tered suspensions was not tested, although this appears to be the 

 more reasonable method of testing the matter. Their experiments 

 with heated soils are of little value, for two reasons. First, the 

 temperature and pei'iod of exposure were excessive for the object 

 in view, namely, the destruction of the protozoa; and, secondly, 

 they ignored the effect of the bacteriotoxins and heat-toxins. As 

 it appeared that a confirmation of their work was necessary, cer- 

 tain experiments were begun with this object. 



In the first, a good arable soil was treated, for two days, with 

 2 per cent, of chloroform, and 20 grm. portions were weighed into 

 small, wide-necked, ounce-bottles. These were divided into two 

 sets. Each portion of one set received four c.c. of a suspension of 

 a ciliate, Colpoda cueullus, while the portions of the other set were 

 treated with the same quantity of the same suspension after it had 

 been heated at 65° for ten minutes. Thus, one set received a sus- 

 pension of living, the other of dead protozoa. The ciliates had 

 been grown in 4 per cent, bean-infusion, and had been derived 

 from a garden-soil. It was not a pure culture, and had been partly 

 washed in 0'2 per cent, saline, but as this caused an encysting of 

 the ciliates, the washing could not be continued until the great bulk 

 of the bacteria had been eliminated. As it was, each portion re- 

 ceived 400 motile forms of Colpoda cueullus, besides many bacteria 

 and encysted ciliates. The bottles were covered with a small bell- 

 jar, and incubated at 28°. In this, and the succeeding two experi- 

 ments, the soils, containing at the start 20-9 per cent, of moisture. 



