HEMATOZO'A (Gr. hcema, blood, and won, a living creature) is the term applied by helminthologists to the entozoa existing in the blood. They occur in mammals, birds, reptiles, fishes, and many invertebrate animals. Some of them belong to the nemato idea, others to the trematoidea, and others to the protozoa. Most of them are micro scopic, devoid of generative organs, and exist in the blood, circulating both in the arteries and in the veins. A very small number attain a considerable size, and are pro vided with organs of reproduction. These larger ones are generally found in some definite part of the circulating system. Thus, for example, in man the distoma hama tobium is almost entirely restricted to the abdominal venous system; in the horse, the sclerostoma aneurysmaticum to the abdominal arterial system; and in the porpoise, the pseudalius filum to the pulmonary artery and its branches.
Nothing definite is known regarding the origin of these parasites, but certain observa tions made upon the hematozoa of the frog by Valentin (and subsequently confirmed by Vulpian), lead to the belief, that some of the more minute forms are the larvm of a worm living in the organs surrounding the vessels. We shall restrict our remarks to the hematozoa occurring in man, the horse, and the dog. By far the most important of human hematozoa is the distoma hamatobium already mentioned. It has only been observed in Egypt, where it is very common, and where it was found by Griesinger 117 times in 363 autopsies. The male, which is the larger of the two, is about three-tenths of an inch in length. The common liver fluke (D. hepaticum) has, in one instance at least, been found in the interior of the portal vein. In the various cases in which dis tomata have occurred in tumors, they must have been conveyed to the places in which they were found by the blood.
In the year 1665 Ruysch discovered a large number of small worms in a dilatation of the mesenteric artery of a horse. Sixty years afterwards, a second case was noticed, and it is now known that such cases are of extreme frequency. These verminous aneurisms of the abdominal arteries occur in the ass and in the mule, as well as in the horse. The worm found in them is the sclerostoma armatum, one of the nematoidea, and often more than an inch in length. It is old horses that are chiefly affected; indeed they scarcely ever seem to escape, for Bayer found these Viniors 48 titnes in the examina tion of 50 worn-out horses. For much very interesting information on this curious sub ject, the reader is referred to Bayer's memoir in the Archly. de _Vaccine comparee for 1842.
In the dog, hematozoa, sufficiently large to be visible to the naked eye are rare. Thirteen such cases are collected by Davainc in his Iraite des Entozoaires, 1860, the worm generally being a filaria. The microscopic larvae of a nernatoid worm are some times found in enormous quantities circulating in the blood of this animal. From the examination of the blood of clogs, Gruby and Delafond believe that 1 in every 20 of these animals presents this peculiarity.
In none of the above cases does the presence of these entozoa appear to affect the general health of the individual in whom they reside, whether he be man, horse, or dog.—For further information on this subject, the reader may be referred to Davaine, op. cit. pp. 308-342, and Vogel's Pathological Anatomy, p. 442, etc.