In May 1912 when on the way with our Floating Laboratory to Rejaf, en route for the sleeping sickness district in what was formerly the Lado Enclave (now part of Mongalla Province), the late Colonel Mathias shot, near Renkwood station on the White Nile, two specimens of the Senegal or red-fronted gazelle—Gazella rufifrons. I found one of these animals, a female in good condition, heavily infected with sarcosporidiosis, the diaphragm, the intercosted muscles and those of the thigh being specially affected, though the striped muscle fibre everywhere contained cysts in varying numbers. In the light of the observations made by Probst and Francis (1910) the blood was carefully examined but no sarcosporidial spores were found in it nor were any blood parasites present.

“Tick paralysis” occurs in British Columbia and affects man, sheep, and probably other animals. The disease is caused by the bites of Dermacentor venustus Banks. It is usually of short duration, is benign in character, but occasionally it persists for long periods, and may terminate fatally. From an economic point of view, the disease is of some importance to the sheep industry. The causative agent has not been discovered, and the disease has not been reproduced by inoculation. The most likely hypothesis is that the tick injects a toxin which gives rise to symptoms appearing coincidentally with the complete engorgement of the tick. In three consecutive cases, experimentally produced by me in lambs, paralysis occurred six to seven days after the ticks were put on. In no case did I fail to produce paralysis through the agency of the tick bites. It has been proved that D. venustus usually bites sheep along the back-bone; possibly the point of attachment may have some bearing on the symptoms or severity of the case. It is probable that other species of ticks may produce a similar disease. No larvae or nymphs were encountered on sheep, and I have no records of their attacking man in British Columbia.

The following observations were made in September, 1908, during a short residence at Aberdeen where, through the kindness of Prof. J. Arthur Thomson, I was able to deal with a considerable number of fishes in the very limited time at my disposal1. The investigation was intended as a continuation of that already carried out at St Andrews, the object being to examine a number of fishes which could not readily be obtained at the latter place. There the fishes dealt with were mostly littoral forms, but at Aberdeen attention was mainly paid to the larger deep-water fish; of these a plentiful supply could be easily obtained. A few species were re-examined here.

The muscular system is so highly developed in the Ixodoidea, that it is no matter of surprise that it has been the subject of more or less detailed treatment in most of the publications dealing with tick anatomy; but, with a single exception, the existing descriptions do not extend beyond a general classification of the various muscles, with the addition of brief remarks, in some instances, on the histological structure of the muscle fibres. In the majority of cases, also, the observations only apply to the Ixodid ticks, and although the general arrangement of the musculature in the two families of the Ixodoidea is not fundamentally different, the comparative anatomy of the muscles offers some difficulty, owing to the great morphological differences which the two families present.

The following note is published by way of supplement to the foregoing paper on “Tick Paralysis” by Hadwen, as it records a positive experiment carried out in Cambridge upon a dog experimentally infested with Dermacentor venustus obtained from Canada.

When, in June 1911, I took over the charge of the Colony and Yaws Hospitals at St George's, Grenada, I learned from the Medical Reports that ankylostomiasis was existent in the Colony—a dozen cases having been treated in the Colony Hospital for this disease during the previous year, and one case having been met and treated in one of the out-districts.

In the course of our studies on species of Rhipicephalus, we have noted the great variability in size and structure observable in the genus. This variability has been a cause of much confusion in classification, as noted by Warburton (Parasitology, 1912, v. 1). It soon occurred to me, in seeking for an explanation of this variability, that it might well be due to nutrition, it being probable that, under natural conditions, a certain number of ticks are removed from the host before they have fed to repletion. When a host is infested with ticks it will brush or rub off a certain number prematurely and the ticks which are imperfectly fed would, doubtless, give rise to adults of small size. As stated, the great variability observed in Rhipicephalus is very striking. In the genus Ixodes, on the other hand, the size of the adults is fairly constant. In the latter case, we have, as a rule, to deal with small ticks provided in the immature stages with long hypostomes, both the small size and hypostomal structure rendering it most difficult for the tick to be removed prematurely from the host. It is difficult to remove Ixodes from the host without breaking the hypostome and using considerable force. In Haemaphysalis, as in Rhipicephalus, the immature stages are provided with short hypostomes and the ticks are more readily removed. The variation in size noted in adult Haemaphysalis, whilst considerable, is not as great as in Rhipicephalus, which would appear to be attributable to the smaller size of the tick, being in a measure a protection against its being prematurely removed from the host.

Rhipicephalus appendiculatus requires three hosts upon which to feed in its larval, nymphal and adult stages. The larvae remain upon the host 3–7 days in most cases; when they remain considerably longer they either do not imbibe blood freely or they may not actually attach themselves on the day on which they were placed on the host; gorged larvae have dropped off the host up to 15 days after the unfed larvae were placed on the host. Nymphs remained upon the host 5–11 days and fertilized replete females abandoned the host after 6–14 days. The males may stay on longer. Unfertilized females may remain upon the host up to 24 days. The temperature at which the host is maintained, within the limits observed, exerts no apparent influence upon the time that the different stages of the tick remain attached. Metamorphosis takes place: from egg to larva in 32–65 days at 17–19° C.; from larva to nymph in 4–6 days at 30° C., in 21–41 days at 15–17° C., in 60–75 days at 13–14° C.; from nymph to adult in 10 days at 37° C., in 21–28 days at 20° C., in 64 days at 14° C. Temperature therefore markedly influences the rate of development. Oviposition commences 6–23 days at 17–19° C. to 50–61 days at 12° C. after the female abandons the host, the process lasting 15–56 days, during which period the female lays 3000–5770 eggs. Unfed larvae and nymphs were still lively after 333 days and 164 days respectively in a tightly corked bottle maintained at room temperature in a darkened cupboard in the laboratory. Unfed adults were lively after 181 days on moistened earth in a gauze covered jar kept in the cupboard; we have one lot of which a few individuals were living (unfed) after 630 days, a single male being still alive after 682 days (21. iii. 13).

It has been pointed out by Warburton (1912) that the degree of variation within the species of the genus Rhipicephalus is very considerable, and in view of this fact it is important to investigate the range of a species and the value of the differential structural characters upon which species are based. The great majority of the Rhipicephali are inornate and this, in conjunction with the general lack of distinguishing structural features and the wide variation found within the species, renders determinations difficult. As Rhipicephalus pulchellus, however, possesses a characteristic and well-marked ornamentation, which is subject to but slight variation, any specimen, at least in the case of the males, may be determined without difficulty.

The diseases included under the general term of piroplasmosis are amongst the most devastating which affect domesticated animals, and they are, consequently, of great economic importance. As far as known, all forms of piroplasmosis are tick-transmitted.