This is the period of greatest disturbance, not only in consequence of the actual presence, but also of the mode of living, of the parasites.
Moussu declares that the parasites live principally on blood, at least during the first and second stage of their sojourn in the liver, adducing as proof that if one completely injects the vascular system of the liver (arteries and veins), some of the injected matter will be found a day afterwards in the digestive apparatus of the parasites.
The disturbances which they produce are therefore due to their actual presence and its consequences, to their mode of life, and to the intercurrent infections of which they are sometimes the initial cause.
It is idle to object that the part played by these parasites is less important than has been suggested, and that the mortality results from intercurrent infection, and not from the parasites themselves. It is equally idle to point out that carcases of animals suffering from severe infection with distomata, particularly the carcases of sheep, are frequently found in slaughter-houses, in perfectly fat condition, and with the appearance of not having suffered in any way. These observations are perfectly correct and well founded. But it matters little that death results from an infection superadded to the distomatosis, if the presence of distomata is the determining factor in causing the superadded infections, and if such infection is, as Moussu believes, almost inevitable in animals already exhausted by the action of the parasites.
The fact that animals suffering from distomatosis and slaughtered for food are well nourished is not a valid objection; for it has long been known that wasting and anæmia are not immediate consequences, and that before they are clearly apparent the distomata must have been present in the liver for several months. Bakewell and the Marquis of Behague have shown that in moderately infected animals there is a tendency to lay on flesh during the first and a portion of the second stage of development of the disease.
If the animals are slaughtered before the period of progressive decline sets in, it is quite possible to form entirely wrong views regarding the importance of these parasites.
The wasting process commences towards the end of the second phase of the disease, and then makes rapid progress. The parasites, which have then been continuously drawing on the blood for their nourishment for a long time, produce anæmia, and some infection of the bile ducts, and usually a certain degree of icterus.
The third phase is accompanied by general signs of cachexia, which need not again be described. They are similar to those of all progressive cachexias. In animals which survive this phase and are ultimately slaughtered the liver always shows very marked sclerosis, commencing around the biliary ducts. Even after the parasites have been evacuated, these ducts appear indurated, thickened, fibrous, and sometimes encrusted with biliary deposits or obstructed with true calculi. These calculi may or may not contain parasites; sometimes they simply contain eggs: they are open, tubular, and perforated, but always irregular on the surface.
When in addition complications have appeared, one usually finds general lesions of septicæmia and blood infection.
In erratic distomatosis, which is of no importance clinically, distomata may become encysted in the lung or other viscus, and in time die. The cysts, which only contain one and rarely two parasites, present a fibrous shell, enclosing a blackish, pultaceous, grumous magma, which sometimes has undergone a certain amount of calcareous infiltration. The parasite may be entirely destroyed.