30 



material. Bracy Clark says that they make an audible snap in doing 

 tliis, but the writer has not heard it. 



Late symptoms. — The chief symptom of the disease caused by these 

 larvte is the catarrhal discharge on the affected side of the nose, which 

 gives rise to one of the popular names of the disease, "snot-nose." 

 Even this symptom may be absent when but few lar\ ;e are present. 



Keumann {Traite des Maladies Parasitaires, 1888, p. 501) accurately 

 describes the symptoms of affected sheep as follows : 



Three or four larvae of CEstrus are frequently found in the frontal sinuses of sheep 

 which, during life, had never manifested any symptom. It is only when these larvie 

 are numerous, and when they are quite well advanced in their development at the 

 commencement of spring-time, that they occasion morbid troubles. The latter hegin 

 by a discharge, often unilateral, which is at first clear and serous, then thick and 

 mucous. Frequently there is sneezing and snorting, accompanied by the expulsion 

 of mucus and sometimes of CEstrus larvfe. Later the animals turn the head back- 

 ward, often shake it, rub the nose against the ground or some other object within 

 reach, or with their front feet. As the malady gradually advances the sheep go with 

 lowered head, lifting the feet high as if they were Avalkiug in water. Sometimes 

 they quickly raise the head, carrying the nose to the wind, and then beud it back- 

 wai'd convulsively. From time to time they stagger and are seized with vertigo, but 

 do not turn in a circle. In severer cases there is difficulty of breathing, the first res- 

 piratory passages being obstructed by the larva) or the inflammation of the mucous 

 membrane. The eyes are red and watery. The disease may be still further compli- 

 cated. The sick lose appetite and rapidly grow poor; they grate their teeth; a 

 frothy saliva runs from the mouth ; their eyes roll in the sockets ; convulsions arise 

 and finally death ensues, sometimes within six or eight days after the appearance of 

 the first symptoms. 



But the disease is rarely so fatal; it lasts longer, and the larvie having been suc- 

 cessfully cast out, the symptoms generally become more favorable and by degrees 

 completely disappear. 



This affection has sometimes been mistaken for "gid, " or "turn-sick," due to Ccc- 

 nurtis cereiralis, whence the name "^ false gid," or vertigo of CEstrus, which has been 

 given to it. Confusion will be avoided by recalling that turning in a circle does not 

 take place in the present disease. The latter is nearly always accompanied by nasal 

 discharge and snortiugs, which do not appear in true " gid, " and which, besides, 

 show themselves only in young subjects. 



Occurrence. — The larvae of CEstrus oris may be found in the nasal 

 cavities throughout the year, and in nearly all stages of growth. This 

 is more especially true of the southern portions of the United States, 

 where the winters are mild and short. During the last winter and 

 spring, in January and March, larvse were collected of all sizes. Those 

 represented by natural-sized figures (Plate I, Fig. 7), were collected in 

 January at an abattoir in Baltimore, Md. Those figured in Plate III 

 were collected in May. From the older of these grubs a pair of flies 

 were hatched. The presence of very young larvje during the past 

 winter is very interesting, and indicates the presence of flies at an un- 

 expected season. The usual time for the appearance of the fly is said 

 to be during the months of June and July, and the usual period of 

 pupation about two mouths. Two of my experiments showed that the 

 time might be three weeks or four weeks exactly. The larv® is said 



