Fig. 38.—Bodo saltans. A, the positions assumed in the springing movements of the anchored form; B, longitudinal fission of anchored forms; C, transverse fission of the same; D, fission of free-swimming form; E1-E4, conjugation of free-swimming with anchored form; E5, zygote; E6, emission of spores from zygote; F, growth of spores: c.vac, contractile vacuole; fl.1, anterior; fl.2, ventral flagellum; nu, nucleus. (From Parker's Biology, after Dallinger.)
The life-cycles varied considerably in length. It was in every case found that after a series of fissions the species ultimately underwent conjugation (more or less unequal or bisexual in character);[[124]] the zygote encysted; and within the cyst the protoplasmic body underwent brood-formation, the outcome of which was a mass of spores discharged by the rupture of the cyst (Fig. 38). These spores grow from a size too minute for resolution by our microscopes into the ordinary flagellate form. They withstand the effects of drying, if this be effected immediately on their escape from the ruptured cyst; so that it is probable that each spore has itself a delicate cyst-wall and an aplanospore, from which a single zoospore escapes. The complex cycle, of course, comprises the whole course from spore-formation to spore-formation. Such complete and regular "life-histories," each characteristic of the species, were the final argument against those who held to the belief that spontaneous generation of living beings took place in infusions of decomposing organic matter.
Previous to the work of these observers it had been almost universally believed that the temperature of boiling water was adequate to kill all living germs, and that any life that appeared in a closed vessel after boiling must be due to spontaneous change in its contents. But they now showed that, while none of the species studied resisted exposure in the active condition to a temperature of 138°-140° F., the spores only succumbed, in liquid, to temperatures that might even reach 268° F., or when dry, even 300° F. or more. Such facts explain the constant occurrence of one or more such minute species in liquids putrefying under ordinary conditions, the spores doubtless being present in the dust of the air. Very often several species may co-exist in one infusion; but they separate themselves into different zones, according to their respective need for air, when a drop of the liquid is placed on the slide and covered for examination. Dallinger[[125]] has made a series of experiments on the resistance of these organisms in their successive cycles to a gradual rise of temperature. Starting with a liquid containing three distinct species, which grew and multiplied normally at 60° F., he placed it under conditions in which he could slowly raise the temperature. While all the original inmates would have perished at 142° F., he succeeded in finally producing races that throve at 158° F., a scalding heat, when an accident put an end to that series of experiments. In no instance was the temperature raised so much as to kill off the beings, so that the increased tolerance of their descendants was due not, as might have been anticipated, to selection of those that best resisted, but to the inheritance of an increased toleration and resistance from one generation or cycle to another.
As we noted above (p. [40]), the study of the Flagellates has been largely in the hands of botanists. After the work of Bütschli in Bronn's Thier-Reich, Klebs[[126]] took up their study; and the principal monographs during the last decade have appeared in Engler and Prantl's Pflanzenfamilien, where Senn[[127]] treats the Flagellates generally, Wille[[128]] the Volvocaceae, and Schütt the "Peridiniales" or Dinoflagellata;[[129]] while only the Cystoflagellata, with but two genera, have been left to the undisputed sway of the zoologists.[[130]]
Among this group the majority are saprophytes, found in water containing putrefying matter or bacteria. The forms so carefully studied by Dallinger and Drysdale belong to the genera Bodo, Cercomonas, Tetramitus, Monas, and Dallingeria. Many others are parasites in the blood or internal cavities of higher animals, some apparently harmless, such as Trichomonas vaginalis, parasitic in man, others of singular malignity. Costia necatrix, infesting the epithelial scales of fresh-water fish, often devastates hatcheries. The genus Trypanosoma, Gruby, contributes a number of parasites, giving rise to deadly disease in man and beast.[[131]] T. lewisii is common in Rodents, but is relatively harmless. T. evansii is the cause of the Surra disease of Ruminants in India, and is apparently communicated by the bites of "large brown flies" (almost certainly Breeze Flies or Tabanidae, Vol. VI. p. 481). T. brucei, transferred to cattle by the Tsetse Fly, Glossina morsitans (see Vol. VI. Fig. 244, p. 513) in Equatorial Africa, is the cause of the deadly Nagana disease, which renders whole tracts of country impassable to ox or horse. Other Trypanosomic diseases of animals are, in Algeria and the Punjab, "dourine," infecting horses and dogs; in South America, Mal de Caderas (falling-sickness), an epidemic paralysis of cattle. During the printing of this book, much additional knowledge has been gained on this genus and the diseases it engenders. The Trypanosomic fever recently recognised on the West Coast has been found to be the early stage of the sleeping-sickness, that well-known and most deadly epidemic of Tropical Africa. Through the researches of Castellani, Nabarro, and especially Colonel and Mrs. Bruce, we know now that the parasite T. gambiense is transferred by an intermediate host, a kind of Tsetse Fly (Glossina palpalis). Schaudinn's full study of a parasite of the blood corpuscles of the Owl has shown that while in its intracorpuscular state it resembles closely the malarial parasites in behaviour, and in its schizogenic multiplication, so that it was considered an Acystosporidian, under the name of Halteridium, it is really a Trypanosoma;[[132]] for the accomplishment of successful sexual reproduction it requires transference to the gut of a gnat (Culex). The germs may infect the ovary, and give the offspring of the insect the innate power of infecting Owls. Thus a new light is shed on the origin of the Coccidiaceae, whose "blasts" in the insect host resemble Trypanosoma in their morphology.
Fig. 39.—Morphology of Trypanosoma. a-f, Stages in development of Trypanosoma noctuae from the active zygote ("ookinete"); b, first division of nucleus into larger (trophic) and smaller (kineto-) nucleus; c, d, division of smaller nucleus and its transformations to form "blepharoplast" and myonemes; f, adult Trypanosoma; g, h, i, Treponema zeemannii of Owl; g, Trypanosome form; h, Spirochaeta form; i, rosette aggregate. (After Schaudinn.)
The human Tick fever of the Western United States and the epizootic Texas fever are known to be due to blood parasites of the genus Piroplasma (Babesia), of which the free state is that of a Trypanosome. It appears certain that Texas fever, though due to Tick bites, is not transferred directly from one beast to another by the same Tick; but the offspring of a female Tick that has sucked an infected ox contains Trypanosome germs, and will by their bites infect other animals. It would seem probable that the virulence of the Persian Tick (Argas persica) is due to similar causes. The Indian maladies known as "Kala Azar" and "Oriental Sore" are characterised by blood parasites, at first called after their discoverer the "Leishman bodies," which have proved to be the effects of a Piroplasma.
Trypanosoma is distinguished by the expansion of its flagellum into an undulating membrane, that runs down the edge of the body, and may project behind as a second lash. In this membrane run eight fine muscular filaments, or myonemes, four on either surface, within the undulating membrane; at their lower end they are all connected with a rounded body, the "blepharoplast," which is here in its origin, as well as in its behaviour in reproductive processes, a true modified nucleus, comparable in some respects, as was first noted by Plimmer and Rose Bradford,[[133]] with the micronucleus of the Infusoria. Part of the segmentation spindle persists in the form of a filament uniting the blepharoplast with the large true functional nucleus (Fig. 39, a-f).
The blood of patients suffering from relapsing fever contains a fine wriggling parasite, which was described as a Schizomycete, allied to the bacteria, and hitherto termed Spirochaeta obermeieri. Schaudinn has shown that this and other similar blood parasites are closely allied to Trypanosoma; and since the original genus was founded on organisms of putrefaction which are undoubtedly Schizomycetes, Vuillemin has suggested the name Treponema. T. pallidum is found in syphilitic patients, and appears to be responsible for their illness.[[134]]