20 
mal with the substance and failing to secure any further trans- 
mission of the disease from the substance of his body. No living 
this poison solution sometimes become, where diphtheria germs 
are cultivated, that a single drop of it will kill a large and healthy 
horse. 
The extent to which the poison is produced under different 
conditions, or the “ virulence” of the germs, is extremely variable. 
This variation is ae in different epidemics and in different 
cases of the same e 
Two quite distinct aetna exist for the production of the 
p ne is the same as that followed by ordinary poiso' 
ous plants, like the toad-stool, or the aconite, belladonna or 
strychnine pla’ n h of these, the poison results as a 
€ poisons can be 
discarded from the plant-bodies only by excretion directly into 
r 
The other method of poison-production is that by which the 
bacteria tear apart the organic substances of the tissues or fluids 
