332 A FURTHER CONTRIBUTION TO THE 
thirty-six hours, during which it is distinctly recorded that the deposit in the 
glass was white, but in the course of the next day ; and it is natural to suppose 
that it was in this medium, in which the form became so greatly modified, and 
at the same time the function of active motion conferred upon the previously 
motionless organism, that the faculty of pigmentary fermentation was also 
acquired. Then, just as modifications of form assumed by a bacterium in any 
one medium are more or less quickly lost when the organism is restored to its 
previous habitat, so should we expect it to be with altered function, and this 
bacterium, when transferred from the Pasteur’s solution to either milk or urine, 
would more or less quickly lose the new fermentative property which it had 
acquired. 
One clear instance of acquisition of a new function by the bacterium is 
presented by the power of active movement which showed itself for the first 
time in the Pasteur’s solution ; so that if we were to adopt the language of some 
authors who have attributed a most exaggerated importance to movement as a 
distinctive character, we should say that the organism was converted in that fluid 
from a bacteridium to a bacterium. But when restored to urine, the organism 
moved but languidly, and after about two days became again motionless. In 
milk, on the other hand, the power of motion was more permanently retained, 
and active movements were observed both in the third and the fourth glass 
of boiled milk as late as five days after the organism had left Pasteur’s solution. 
There is another consideration which seems strongly confirmatory of the 
argument against a distinct ‘ pigment bacterium’ as the cause of the black 
deposit in the milk. If it were true that such an organism existed, which, 
when introduced along with the lactic-acid ferment, would produce this striking 
effect, black milk would be a thing of frequent occurrence ; whereas this is, 
so far as I am aware, the first time such a thing was ever seen. But if it be 
asked, Why was it that this unheard of appearance showed itself in my experi- 
ment ? the answer is that the conditions of the experiment were such as to 
afford the organism opportunities which it had probably never had before. 
Never before, in all probability, was this organism allowed to develop unmixed 
with any other in urine and Pasteur’s solution consecutively. For while this 
ferment takes the precedence of others in milk, such is far from being the case 
in urine, and very probably in Pasteur’s solution also. How far the previous 
residence in urine may have predisposed this bacterium to assume the pig- 
mentary fermentation in Pasteur’s solution, further experiment can alone decide. 
Suffice it to say, meanwhile, that the conditions under which the organism 
grew were novel, and therefore novel appearances need not surprise us. The 
case seems exactly parallel to that of Bacterium No. I. Never before, perhaps, 
