The dwarf tapeworm (Hymenolepis nano) is the most numerous parasite of this group found in man in North America. It is regarded by some as identical with a species that oc curs in rats and mice. On account of its small size it was not discovered until the middle of the last century and i while even yet it is fre quently overlooked t is present at times in enormous numbers. It may justly be considered cosmopolitan in its distribution. Cases occur in general under unfavorable hygienic sur roundings and infection is probably traceable to contamination of food by rats and mice. The worms are usually found in considerable numbers and excite digestive disturbances of marked severity. Diagnosis is made by micro scopical demonstration of eggs in the faces and treatment should be at the hands of a physician. The records of Ransom concerning North American cases indicate the great frequency of the parasite in children and especially in infants.
One of the smallest of tapeworms is Tamia echinococcus which is a parasite of the dog. The chain consists of only three or four proglottids. The parasite is important because of the character of its larva or bladder-worm which is known as an hydatid (Echinococcus polymorphus), This bladdier-worm develops in a very large number of hosts and produces a'complex structure with secondary and tertiary bladders in great numbers so that the entire mass assumes enormous proportions. Speci mens found in the human host have attained a mass equal to 30 or 40 pounds. The liver is the preferred seat of the bladder worm in man and its serious character depends upon this fact because the tissues involved may be of a character to prevent surgical treatment and bring about the death of the host. In addition to the general practice of removing the hydatid by surgical means other methods of treatment have recently been tried with some success. This and numerous other parasites owe their.
abundance and distribution to the frequence and movements of stray dogs.
The broad tapeworm, Dibothriocephalus lotus, is also known as the fish tapeworm of man. The adult occurs in the small intestine of man and of the dog. The larva is found in the muscles and viscera of numerous fish: pike, hurbot, grayling and trout. This is the largest common human parasite, reaching often a length of 20 meters. The head (Fig. 4) is provided with a pair of lateral sucking grooves which distinguish it readily from the other forms discussed previously. The uterus forms a rosette (Fig. 5) in the thickened centre of the proglottid and the species is recognized readily by both of these features. The para site is very abundant about the shores of the Baltic and also occurs in isolated spots as around a lake near Munich and in the vicinity of Lakes Geneva, Neuchatel and Bienne in Switzerland. Lame have been found abun dantly in fresh fish from markets near the Baltic and living specimens were obtained from smoked, salted and frozen fish as well as from salted roes used as caviar. The species is com mon in Japan and perhaps in some other parts of Asia where the larval host is said to be a salmon eaten raw as a delicacy by the natives. It has been introduced many times into the United States and seems to have established itself in small areas around certain lakes in northern Michigan, Wisconsin and Minnesota where an abundant foreign population has in troduced from the Old World the habit of eat ing smoked fish without cooking. For further data consult Nuttall, G. H. F., Poisons Given off by Parasitic Worms in Man and Animals' (American Naturalist, Vol. XXXIII, 1899, pp. 247-49) ; Stiles, C. W., and Hassall, Albert, The Inspection of Meats for Animal Parasites' (United States Department of Agri culture, Bureau Animal Industry, Bull. 19) ; Ward, H. B., 'Cestodes in Reference Handbook of Medical Sciences' (New York 1913).