|} April 6, 
Lockington,]} 
The role of microscopic parasites is probably similar to that of the more 
tangible teniw and other worms that live as commensals within the body, 
devouring the nutriment intended for it; or, at the very worst, they are 
feeders upon the secretions of their host. In either case, they are fed at i 
| his expense. To one in thorough health they do little harm, but become 
a burden to those of weaker powers, and may become, in those attacked hf 
with a grave disorder, so diseased themselves that they may act as car- 
riers of the disease to previously healthy bodies. 
The power possessed by these parasites, taken from the victim of an 
infectious disease, of producing descendants which, for several generations, : 
are capable of reproducing that disease, is often pointed to as a proof both | 
of the specific nature of the parasite, and of its potency as the primary | 
cause of the disease. | 
Yet these facts, when looked at properly, tend to prove the reverse. | 
The presumably toxic microbes, removed from their accustomed pabu- 
lum, reproduce themselves, it is true, in healthy infusions, which by their 
presence are rendered toxic, but at each removal to a fresh environment 
some of the toxic power is lost, until at last the virus has become so at- 
tenuated that it can safely be used asa medium of inoculation (as has 
been practised largely by Pasteur upon domestic animals) reproducing 
the original disease ina mild form, and thus (in some way not easy to | 
| explain) ensuring the subjects treated with it against the fatal form of the 
| disease. 
| What is this gradual enfeeblement of the toxic powers of the parasite 
1 | but its gradual return toward its normal condition—toward the neutral 
properties and probably toward the external appearance presented by its 
| ancestors when they dwelt within a healthy animal ? 
| Let the cultivation proceed for a sufficient number of generations, and 
I | the reversion will be complete. 
Observers, principally chemists, who have studied the microbes of dis- 
sase, have figured their forms, and in some cases have registered the trans- 
formations of a generation ; but much more than this is necessary to prove 
their specific distinctness, or their direct connection with the disease. 
If, after an examination of hundreds of individual animals, some in 
health, others in every stage between health and the crisis of the disease, 
and others in the various stages of recovery, no transition form is in any 
one instance noted—no microbe intermediate in character between that of 
health and that found in the disease ; the evidence, though still negative, | 
will be in favor of the ordinary germ theory, but if in only one animal | 
among hundreds intermediate forms are found, that one instance will be 
positive evidence in favor of the views here advocated ; since the diseased 
form, when once produced, can reproduce its characters for several gen- 
erations. 
Microscopic examinations of the cultured organisms up to the hundredth 
generation would throw some light on the subject. 
