341 
of ordinary distilled water is acquired after distillation, either 
by mixture with extremely small quantities of other waters, 
or by contact with the surface of the vessels in which it is 
contained. It was also evident that between waters of dif- 
ferent kinds and of different sources there are corresponding 
differences in the degree of zymotic effect they produce, 
whence it seemed probable that a practical method of 
judging of the amount of zymotic impurity contained in 
any two waters might be founded on the comparison of the 
degree of opalescence produced by each in the same time 
and at the same temperature. In how far this surmise was 
justified may be judged of by the results of experiments to 
be hereafter referred to, relating to the zymotic powers of 
the waters supplied to the metropolis. 
If the apparently inevitable contamination of originally 
pure water, when kept, is due not merely to admixture with 
other water, but also to contact with surfaces impregnated 
with living matter, it becomes of interest to inquire by what 
conditions the action of such surfaces is limited or determined. 
In the course of one of the observations already related it 
was observed that a boiled liquid contained in a superheated 
test glass, which had long remained perfectly limpid, and 
entirely free from organic forms, became turbid after a pipette 
employed in order to procure a specimen for ie i 
examination had been dipped in it; and that the time which 
intervened corresponded with that which usually elapses after 
impregnation before the effect manifests itself. This occur- 
reuce suggested the following experiments, which were under- 
taken in order to ascertain how far it is necessary that a 
surface should be moist in order to its acting zymotically. 
MVIL, J anuary 30.—A glass rod was charged with 
bacteria by dipping it into a solution on the surface of which 
there was a viscous scum, consisting entirely of these bodies 
imbedded in gelatinous matrix. The rod was allowed to dry 
in the air for a few days; it was then introduced into boiled 
test solution contained in a superheated glass. On February 
6 the liquid was already milky and teemed with microzymes. 
On the same day a portion of the same scum was introduced 
into a test glass and dried with a gentle heat. The glass 
was then filled with test solution which had just before been 
boiled and cooled in the usual way. The result was the same 
as in the previous experiment. 
In these instances it may be readily understood that the 
drying was very imperfect. To determine the effect of more 
complete desiccation, an eprouvette containing one cubic 
centimetre of cold water previously ascertained to be zymotic, 
