These all belong to the lowest forms of plants, the fungi, and unless collected together in redundant growth, they are too minute to be cognizable with the naked eye.

Respecting their origin by propagation through sprouts and sporules hardly a doubt can exist, and as little as to their translation upon and into the organism; although only in a few instances has it been possible to certify this by direct evidence.

It is obvious that certain conditions are requisite for the harboring and the evolution of these germs. This often manifestly consists in pathological conditions, and, at the same time, often in processes of decomposition (fermentation, putrefaction). In the great majority of instances, however, we are in the dark concerning those conditions, and the success of our experiments is dependent upon chance. The former contingency is exemplified in fungi upon muco-membranous exudates, sloughs, and upon mortifying patches of the common integument.

The relation of the vegetable parasite to the concurrent morbid condition varies. The latter sometimes stands in that of a pre-existent state, favorable to the development and multiplication of the fungi; at other times the parasite, harbored through influences unexplained, may become the cause of textural disease; for example, inflammation, suppuration, decadence and loss of hair, etc.

Herewith, the injury they inflict upon the organism terminates. Still they may, where they vegetate extensively, become further mischievous by increasing or specifically modifying some process of decomposition. We may instance the fungi of aphthae.

If we except the torula cerevisise in the contents of the stomach and intestines, the torula of diabetic urine, and perhaps, Goodsir's sarcina ventriculi (possibly an infusorium1), parasitic plants, in man, affect the common integuments and mucous membranes only.

With their buds shooting out into more or fewer long, linked, branched threads, they present the form of the thread-fungus.