of Bacteria and their Allies by FHeterogenesis. 385 
interior of certain vegetables or fruits after they have been 
submitted to various unnatural conditions, the question will 
not be whether we have had to do with the wakening up of 
latent pre-existing germs, but rather whether the organisms 
found are results of an infection that has recently been brought 
about—that is, during the exposure of the vegetables or fruits 
to the experimental conditions. And this brings us to the 
consideration of the second of the two possibilities above 
referred to. 
(6) The second possible mode of accounting for the presence 
of microorganisms in the tissues of healthy animals and plants 
is that they have resulted from some process of infection 
brought about antecedently or during the continuance of the 
experimental conditions to which they have been subjected *. 
It is of great importance for the proper consideration of 
this possibility that we should have some definite knowledge 
as to the power possessed by such microorganisms as Bacteria 
and their allies of penetrating the healthy tissues of plants 
and animals, as to the means by which they are enabled to 
do so, as well as concernirg the time needed for such an 
operation. Fortunately one such investigation, very much 
to the point, can be referred to. 
M. C. Potter} has carefully investigated a bacterial disease of the 
turnip which he calls “white rot,” due to infection by an organism named 
Pseudomonas destructans. We shows that this Bacterium “secretes an 
enzyme which dissolves the middle lamella and causes the softening and 
swelling of the cell-wall,” and also a toxin. Later, he enters into details 
as to the mode in which the Bacterium attacks and penetrates the cells 
of the turnip, the latter process being actually seen f. These later obser- 
vations were made upon a small fragment of turnip inoculated with a 
pure culture of P. destructans and introduced into a hanging drop. The 
influence of the Bacteria was very rapidly brought about. One particular 
cell attacked by the Bacteria was watched ; a wall common to it and the 
next was measured, and after half an hour it was found to be nearly twice 
as thick as before; in another twenty minutes it was nearly three times 
* I say “antecedently,” because the explanation favoured by Burdon 
Sanderson of the finding of swarms of Bacteria in kidney, spleen, and 
liver in his experiments previously referred to is some process of infec- 
tion from the alimentary canal. How the infection is brought about he 
does not think it necessary to explain (see Brit. Med. Journal, 1878, i. 
p. 120)—that is, how the Bacteria (not to speak of their germs) could 
penetrate all the coats of the intestine and the capsules of the abdominal 
organs; nor why, if Bacteria or their germs could be active enough and 
have the power of effecting such a migration, they should, on arrival in 
this or that organ, lose all their activity and pass into a “latent condition,” 
+ Proceed. of Roy. Soe. vol. lxvii, p. 442. 
{ Loe. cit. vol. Ixx. p. 392. 
