Not one of these theories would ever have been broached had their authors been aware of two important circumstances. 1. That M. Schreiber, the director of the Museum at Vienna, has proved that worms and their ova are not capable, under ordinary circumstances, of resisting the action of the digestive organs, and, therefore, that they cannot be introduced into the body by this channel. "During six months, he fed a pole-cat almost exclusively on various kinds of intestinal worms, and their eggs mixed up with milk; and on killing and examining it, at the end of this period, not a single worm of any kind was found in it."[37] The reader may perhaps object to this illustration, on the ground that there is so vast a difference between a sheep and a pole-cat, that a comparison in regard to their digestive habits cannot possibly hold good, but if he will turn to paragraph (96), he will see that the stomach of a sheep is as well fitted as that of a carnivorous quadruped for the digestion of animal matters. 2dly, the fluke worm has been found by Frommen in the foetus of the sheep, into which it could not have been conveyed by transmission from the mother, as there is no direct vascular communication between the foetal and maternal side.
[37] Cyclopedia of Practical Medicine, Vol. iv. p. 524.
From a consideration of all these data, the conclusion must at once be drawn, that as living flukes cannot reach the liver from without, they must of a necessity be produced only in particular states of the animal they inhabit. How they originate we cannot of course determine, and this is not the place to hazard physiological conjectures; but it will be found that their appearance in the bile is always preceded by tuberculous deposits in the lungs or liver. This I have proved by numerous dissections, in which I have occasionally found tubercles without flukes, but never met with flukes where I did not at the same time discover tubercles. Fluke worms, therefore, can never be regarded as a cause of rot, they must be looked upon merely as a symptom. We cannot, however, say that tubercles give rise to the liver-fluke, for tubercles are often present in cases where flukes are absent; and if the latter were the effect of the former, their presence under such circumstances would in all probability be constant.