Part 13

_Thorax._—The pronotum is without a ctenidial comb, and has one row of about 14 bristles. The mesonotum, the broadest of the three thoracic nota, also has a single row of about 12 bristles. The metanotum has a single row of about the same number. The mesosternite contains about 5 bristles. The pleura of the metathorax is normally divided. The sternum contains 2 bristles, 1 anterior and 1 posterior. The episternum contains 1 bristle, and the epimerum contains 2 rows of bristles, an anterior row of 7 and an apical row of the same number.

_Abdomen._—The first abdominal tergite contains 2 rows of bristles, an anterior and a posterior of about 6 bristles each, while the next 6 contains but a single row of about 14 bristles each, the lowest placed just below the stigma. From the seventh tergite springs a single antipygidial bristle. The sternites contain a single row of 8 or 10 bristles.

_Legs._—The fore coxa is normally clothed. The fore femur has on its outer surface about 8 fine bristles. The mid femur has a single row of about 6 bristles, while the hind femur has a row of the same number. The hind coxa has on its inner surface a regular row of about 6 teeth. The hind tibia has on its posterior border 5 groups of spines in pairs, while on its outer surface there are about 8 small bristles in a row. The apical bristle on the second tarsal joint of the hind leg reaches to about the middle of the fifth tarsal article. The fifth tarsal article on all of the legs has 4 lateral spines and a subapical pair of hairs.

_Modified segments._—(♂) The manubrium of the claspers is short and narrow. There are two free processes, the upper one, the finger, being broadest and wider at the tip than at the base, its upper border being more convex than the lower border and containing a number of bristles. The ninth sternite is club-shaped, is nearly straight on its dorsal margin, and the ventral margin contains a row of fine bristles from base to apex.

(♀) No bristles in front of the sensory plate. Along its apical margin externally there is a row of about 12 long bristles, and internally a row of less numerous, shorter bristles. Laterally there is a more or less regular row of about 8 bristles, and between this row and the apical row 3 or 4 more.

DESCRIPTION OF PLATE IV. ────────────────────────────────────────────┬────────────────────── Fig. 1. Clasping organs, male. │10 T Tenth Tergite. „ │10 St Tenth Sternite. „ │P Process. „ │F Finger. „ │M Manubrium. „ │IX St Ninth Sternite. ────────────────────────────────────────────┼────────────────────── Fig. 2. Head of female. │ Fig. 3. Last tarsal joint of hind leg. │ ────────────────────────────────────────────┼────────────────────── Fig. 4. Terminal abdominal segments, female.│8 T Eighth Tergite. „ │8 St Eighth Sternite. „ │10 T Tenth Tergite. „ │10 St Tenth Sternite. „ │Sp Spermatheca. ────────────────────────────────────────────┼────────────────────── Fig. 5. Hind tibia. │

CTENOPSYLLUS MUSCULI Dugés.

[Plate IV.]

_Head._—The frons is prominent anteriorly, giving the head somewhat the shape of a fez. There are 4 spines on the posterior border of the gena. The antennal groove reaches to the top of the head. The maxillary palpi are shorter than the labial palpi, which reach to about two-thirds of the fore coxa and are 5-jointed. Maxilla triangular. Eyes absent. At the most prominent part of the frons anteriorly there are two short thick spines, while below these, running along the anterior margin, there are 5 bristles. Above there is an oblique row of 4 bristles, with 1 more placed near the top of the antennal groove. Between this oblique row and lower bristles there are numerous fine hairs. On the occiput there is a subapical row of about 7 bristles on each side, while in front of this are 3 oblique rows of bristles, the first containing 3, the second 4, and the third 5. On the posterior margin of the antennal groove there are several small hairs. On the first joint of the antenna there are about 3 hairs, while on the second joint there are 4 or 5, the longest somewhat longer than the third joint.

_Thorax._—The pronotum has an anterior row of about 10 bristles, and a ctenidium of about 24 spines. The mesonotum contains about 4 rows of bristles, more or less regularly disposed, each row consisting of about 8 or 9 bristles. The metanotum has 2 rows of bristles, a posterior row of about 10 bristles, and an anterior of the same number, while there are several smaller bristles in front of this. The mesothorax contains about 10 bristles. The episternum of the metathorax has 2 bristles, and on the sternum there is 1 large one. The epimerum has 2 rows of 4 bristles each, with 1 large one at the apical margin.

[Illustration:

PLATE IV.

CTENOPSYLLUS MUSCULI, DUGES. ]

_Abdomen._—The first abdominal tergite has 2 rows of 10 bristles each, the posterior being comprised of the larger bristles. The next 6 tergites have 2 rows of bristles each, a posterior of large bristles, about 12 in number, and an anterior of smaller bristles, also 12 in number. On the apical edge of the metanotum there are 2 small teeth on each side. The first abdominal tergite contains 3 such teeth while the second and third have 1 each on each side. At the apex of the seventh tergite in the female there are 4 antipygidial bristles, sometimes 5. The male has but 3 antipygidial bristles. The abdominal sternites from the third to the sixth have a single row of 6 bristles. The seventh has a row of about 16 bristles.

_Legs._—The fore coxa has about 32 large bristles more or less regularly disposed in 6 oblique rows. The hind coxa is without teeth on the inner surface. The mid femur is without bristles on its lateral surfaces. The hind femur is also without a row of bristles on its lateral surfaces. The spines on the posterior border of the tibia are single and in a close set row. The apical spines of the second tarsal joint of the hind legs are shorter than the third joint. The last tarsal joint on all the legs contains 4 lateral spines and a subbasal pair situated between the first lateral pair.

_Modified segments._—(♀) Just beneath the pygidium is 1 long bristle. On the eighth tergite there is a patch of hairs, 6 of which are on the apical margin and about 5 or 7 anterior to these. The stylet is short, almost as wide at the base as at the tip, where there is a long hair. Posteriorly to this bristle there springs another one from the under surface.

(♂) Manubrium of the claspers is narrow, curved at the tip. The finger reaches to the level of the process, has a stout pedicle, is flat on its anterior border, and is decidedly convex on its posterior border, where there are 4 bristles. The shape of the ninth sternite is shown in the figure.

DESCRIPTION OF PLATE V. ────────────────────────────────────────────┬────────────────────── Fig. 1. Clasping organs of male │P Process. „ │F Finger. „ │M Manubrium. „ │IX St Ninth Sternite. ────────────────────────────────────────────┼────────────────────── Fig. 2. Head of female. │ ────────────────────────────────────────────┼────────────────────── Fig. 3. Terminal abdominal segments, females│8 T Eighth Tergite. „ │8 St Eighth Sternite. „ │10 T Tenth Tergite. „ │10 St Tenth Sternite. „ │Sty Stylet. „ │Sp Spermatheca. ────────────────────────────────────────────┼────────────────────── Fig. 4. Hind coxa, inner surface. │

PULEX IRRITANS Linnæus.

[Plate V.]

_Head._—Evenly and abruptly rounded in both sexes. Frontal notch absent. Eye large. Maxillary palpi longer than the labial palpi. Labial palpi reach to about half the length of the anterior coxa and are 4-jointed. The mandibles are broad and markedly serrate. Maxillæ triangular. Antennal groove short and wide, closed behind, thickened on edges, and reaches to top of head in both sexes by chitinous thickening. Second joint contains 8 or 9 fine hairs, shorter than the third joint. Division of the third joint only to be seen on dorsal surface. Two bristles on the gena, one placed low down just above the maxilla, the other below the eye. From the lower margin of the gena occasionally may be seen a small tooth. One bristle on the occiput near the posterior lower angle. A few fine hairs on the posterior edge of the antennal groove.

_Thorax._—The thoracic nota each contain a single row of about 10 or 12 bristles. There is no ctenidium on the pronotum. The mesosternite is narrow and is not divided by an internal incrassation. The episternum of the metathorax is large and contains about 2 or 3 bristles and is not quite separated from the sternum anteriorly. The epimerum has an anterior row of about 7 or 8 bristles and an apical row of about 6.

_Abdomen._—Each of the abdominal tergites, with the exception of the first, has a single row of 8 or 10 bristles. The first has 2 rows of about 4 each. The sternites from third to seventh have a single row of about 6 bristles. There is one short antipygidial bristle on each side.

_Legs._—The hind coxa has on its inner surface posteriorly a number of fine hairs, while anteriorly there are 10 or 12 teeth in an irregular line. The hind femur has on its inner surface a row of about 8 or 9 bristles. The spines on the posterior tibia are in pairs, and there are about 7 bristles in a line on its outer lateral surface. The apical bristle of the second tarsal joint of the hind leg reaches to about the middle of the fifth joint. The last tarsal joints of all the legs contain 4 lateral spines and a subapical pair, and between the third and last lateral spine there is a hair.

_Modified segments._—(♀) The eighth tergite has no bristles above the pygidium but has numerous short stout bristles laterally and on and close to the apical margin. The stylet is short and stout and has at its tip a long hair. The tenth sternite and tergite contain numerous fine hairs, those on the sternite confined to the apical edge.

(♂) The male claspers are quite characteristic. The manubrium is large and curved and points ventrally. The claspers have two processes, the lower of which, with the finger, form together a kind of claw which is covered by the other process forming a flap, quite hairy on its upper margin. The ninth sternite is described very well by Rothschild[208] as “boomerang” shaped. The eighth tergite has a small manubrium.

[Illustration:

PLATE V.

PULEX IRRITANS, LINNÆUS. ]

DESCRIPTION OF PLATE VI. ────────────────────────────────────────────┬────────────────────── Fig. 1. Clasping organs of male │F Finger. „ │M Manubrium. „ │IX St Ninth Sternite. ────────────────────────────────────────────┼────────────────────── Fig. 2. Head of male. │ ────────────────────────────────────────────┼────────────────────── Fig. 3. Terminal abdominal segments, female │8 T Eighth Tergite. „ │8 St Eighth Sternite. ────────────────────────────────────────────┼────────────────────── Fig. 4. Hind coxa and femur, inner surface. │

CTENOCEPHALUS CANIS Curtis.

[Plate VI.]

_Head._—Strongly and evenly rounded in both sexes. Eye large. Maxilla triangular. Maxillary palpi about as long as labial palpi. Labial palpi reach to two-thirds of anterior coxæ, 4-jointed. Seven spines along the lower margin of the gena. The posterior angle of the gena ends in a small tooth. Occasionally this may be absent. Antennal groove in the female reaches to within one-third of the top of head and is prolonged upwards by a chitinous thickening and in the male reaches almost to top of head. Two bristles on the gena, one placed well toward the anterior lower angle and the other in front of the eye. Usual number of bristles on posterior margin of the head, with 2 large ones back of the antennal groove. About 8 hairs on the second joint of the antenna nearly as long as the third joint.

_Thorax._—A row of about 10 bristles on the pronotum, with a ctenidium of about 14 to 16 spines. Two rows of bristles on the mesonotum, a posterior of about 12, another of more numerous smaller bristles placed well anteriorly. The metanotum contains a single row of about 10 or 12 bristles. The episternum of the metathorax has 3 or 4 stout bristles, while the epimerum contains an anterior row of about 10 bristles and a posterior row of about 9.

_Abdomen._—The first abdominal tergite contains 2 rows of about 4 bristles each, while the other tergites to the seventh contain a single row of from 12 to 16 bristles. The stigmata are large. There is a single antipygidial bristle on each side. The sternites from third to seventh have a single row of 4 bristles each.

_Legs._—The hind coxa has on its inner side a patch of from 6 to 12 spines, while the hind femur has a row of 10 or 12 bristles on its inner surface. The spines on the posterior border of the hind tibia, with the exception of the apical, are in pairs, while in the apical group are about 3 stout bristles. The apical spine of the second joint of the hind leg reaches to nearly the middle of the fifth joint. On the fifth joint of all the legs there are 4 lateral spines and a subapical pair, and between the third and fourth lateral spines there is a hair.

_Modified segments._—(♀) The eighth tergite has no hairs back of the stigma. The apical margin is rounded at the apex and contains 8 or 10 bristles. The stylet is short and wide and contains at its tip a long and a short bristle.

(♂) The manubrium is short and narrow. The movable finger of the clasper is short, thick, swollen at its middle, bluntly rounded at its extremity, and contains on its upper border numerous hairs and a few on its lower border.

Rothschild[209] has pointed out certain differences between the _Ctenocephalus canis_ and _Ctenocephalus felis_. The differences are that in the female of the felis the head is longer and more pointed. This difference is not so pronounced in the male. Also certain differences in the shape of the claspers and the number of bristles in the episternum and epimerum of the metathorax and the hind femur, those in the _C. canis_ being more numerous. Also that group of bristles on the posterior border of the hind tibia between the fifth pair and the apical bristles consists of two in the _Ctenocephalus canis_, while there is but a single bristle with a small hair in the _Ctenocephalus felis_.

REFERENCES.

Endnote 201:

1909, McCoy.—“Plague Bacilli in Ectoparasites of Squirrels.” Public Health Reports, Vol. XXIV, No. 16.

Endnote 202:

1908, Schumann.—“A Disease of Rats Caused by Mites.” Centralblatt f. Bact., Oct. 30th.

Endnote 203:

1909, McCoy and Mitzmain.—“An Experimental Investigation of the Biting of Man by Fleas Taken from Rats and Squirrels.” Public Health Reports, Vol. XXIV, No. 8.

Endnote 204:

1908, McCoy.—“A Report on Laboratory Work in Relation to the Examination of Rats for Plague at San Francisco, California.” Public Health Reports, Vol. XXIII, No. 30.

Endnote 205:

Wagner.—Aphanipterologische Studien aus dem zootomischen laboratorium der Universität zu St. Petersburg.

Endnote 206:

1908, Mitzmain.—“How a Hungry Flea Feeds.” Entomological News, December.

Endnote 207:

1908, Miller.—“Hepatazoon Perniciosum (N. G. N. SP.). A Hæmogregarine Pathogenic for White Rats; With a Description of the Sexual Cycle in the Intermediate Host; A Mite (Lælaps Echidninus).” Bull. No. 46, Hyg. Lab. U. S. Pub. Health and Mar. Hosp. Serv., Wash.

Endnote 208:

1908, Jordan and Rothschild.—“Revision of Non-Combed Eyed Siphonaptera.” Parasitology, Vol. I, No. 1.

Endnote 209:

1901, Rothschild.—“Notes on Pulex canis, Curtis, and Pulex felis, Bouché.” Entomologist’s Record, Vol. XIII, No. 4.

1905, Rothschild.—“Some Further Notes on Pulex canis, Curtis, and Pulex felis, Bouché.” Novitates Zoologicae, Vol. XII.

[Illustration:

PLATE VI.

CTENOCEPHALUS CANIS, CURTIS. ]

RODENTS IN RELATION TO THE TRANSMISSION OF BUBONIC PLAGUE.

By Surgeon RUPERT BLUE,

_United States Public Health and Marine-Hospital Service_.

Man has associated the rat with bubonic plague since the dawn of history. The monuments and coins of the earliest times yield abundant evidence of this association. Æsculapius, the god of the healing art, is represented by the Greeks with a rat at his feet. An early scriptural reference may be found in the first Book of Samuel in the fifth and sixth chapters. The historian records therein the occurrence of a fatal epidemic of “emerods” in the land of the Philistines coincident with an invasion of “mice.”

The inhabitants of southern China in recent times have learned to look upon the finding of sick and dead rats in their homes as a harbinger of evil, in fact, as a forerunner of that dread scourge—“wan-yick,” or plague. In the villages and cities of the Kwantung and Kwangsi provinces, as recorded by medical missionaries, epizootic plague almost invariably precedes an outbreak among human beings. So well is this fact known to the common people that many seek safety in flight, feeling assured that in a short time “yang-tzu” or “wan-yick” will claim a harvest of victims among those who remain.

Doctor Mahē, sanitary officer for the port of Constantinople, in 1889, called attention to the fact that epidemics of plague were always announced by a great mortality among rats and mice. In 1894 Yersin reported the fatal epizootic among rats then prevailing in Canton and Hongkong coincident with the outbreak of plague among the Chinese. Recent researches have confirmed these observations and a great deal has been added to the literature of plague, especially in relation to its mode of transmission. Indeed, it should be said that wherever the disease has prevailed in recent years the relation of rats to its spread has been observed, and that since the discovery of the specific bacillus by Yersin and Kitasato, in 1894, bacteriological investigations have shown that there is no difference morphologically or culturally between the bacilli of human and rat plague. Moreover, the gross and microscopic lesions in the lymph nodes are practically the same, and the _B. pestis_ recovered in both fulfills the postulates of Koch.

Nothing was definitely known, however, of the mode of transmission of the disease from rat to rat or from rat to man until the completion of the experimental work of the Indian Plague Commission. Simond, Ogata, Thompson, and Koch each expressed the belief that the infection was transferred by the rat flea. Nuttall (1897) and Simond (1898) demonstrated the presence of _B. pestis_ in the bodies of bugs (_Cimex_) and fleas which had been taken from plague-sick rats, and the latter observer, in the same year, succeeded in transmitting the disease from rat to rat without contact.

The work of the Indian Plague Commission was undertaken (1905) with a view to establishing the exact relationship between epizootics among rats and epidemics among men, and included both field and laboratory observations. The experiments of Gauthier and Raybaud (1903) and of Simond were repeated on a larger scale and greatly improved in that all rats and fleas used were first identified as to species. The findings of the commission may be briefly summarized as follows: That fleas and bugs taken from plague-sick rats contain _B. pestis_, and that some of them remain alive in the bodies of the insects from five to sixteen days; that plague is conveyed by the bites of fleas which have previously fed on the blood of animals suffering with the disease; that rat fleas bite man; that under experimental conditions the infection is not transferred from rat to rat in the absence of fleas.

A careful study of the findings of the workers in India justifies the assumption that plague is a disease of the rodent primarily and accidentally, and secondarily a disease of man. An analysis of the epidemiological facts collected in San Francisco leads to the same conclusion. As a result our practice with regard to suppressive measures and quarantine procedure has undergone a radical change in the last decade. If the infection is flea-borne from rat to man in the majority of cases, then the extermination of the rat should be the first principle upon which to base a campaign. In the former contribution on the subject (1907) I stated that “if we destroy the host there is no longer danger of infecting the parasite.” This basic principle has been recognized and successfully applied in two campaigns against plague in San Francisco. First in the outbreak in Chinatown in 1903–4, and again in the larger epidemic of 1907.

The outbreak of 1907 began May 27, a little over a year after the great fire and earthquake, but no cases were discovered between that time and mid-August when the disease began to appear in various parts of the city. The source of infection was, in all probability, a recrudescence from a focus which was not destroyed in the campaign of 1903–4. There occurred 160 cases with 77 deaths, the last case appearing January 30, 1908. The following table shows the incidence of human plague:

─────────────────────┬───────┬─────── Year. │Cases. │Deaths. ─────────────────────┼───────┼─────── 1907. │ │ May │ 1│ 1 August │ 13│ 6 September │ 56│ 25 October │ 34│ 25 November │ 41│ 12 December │ 13│ 7 1908. │ │ January │ 2│ 1 ─────────────────────┼───────┼─────── Total │ 160│ 77 ─────────────────────┴───────┴───────

EPIDEMIOLOGICAL OBSERVATIONS IN SAN FRANCISCO.

Abundant epidemiological data associating the rat[AE] with plague have been collected in San Francisco. For the purpose of illustration a detailed reference to a few cases will be made. Two small boys (October, 1907) while playing in an unused cellar found the body of a dead rat. The corpse was buried with unusual funeral honors. In forty-eight hours both were ill with bubonic plague. A laborer finding a sick rat on the wharf picked it up with the naked hand and threw it into the bay. He was seized three days later with plague. Doctor C. and family lived in a second-story flat over a grocery store in the residence section. Being annoyed for some days by a foul odor the doctor caused the wainscoting around the plumbing to be removed. One or two rat cadavers were found in the hollow wall. In two or three days the two members of the family who used the room sickened, one dying on the fifth day of cervical bubonic plague. It is probable that infected rat fleas were set free by the removal of the wainscoting.

Footnote AE:

_M. norvegicus_ and _M. rattus_.

Dead rats were frequently found in or near houses where plague had occurred. Immediately upon the discovery of a case of plague trained men were sent into the neighborhood and a thorough search made for rats. This work consisted in the removal of defective wooden floors and walls of insanitary buildings and other harboring places. Extensive rat catacombs were frequently found in these operations. In the yard of a house in which 4 cases had occurred 20 cadavers were found under the board covering. In the walls of a Chinese restaurant 87 dead rats were uncovered.

Very little can be said of the relation of mice (_M. musculus_) to the epidemic. While many thousands were trapped, only a few hundred were examined microscopically and in these no infection was found. They are nonmigratory in habit and for this reason are not considered of much importance from an epizoological standpoint.

Transmission from man to man was observed in but a small percentage of cases, 3 per cent to be exact. In these the probability of transference by fleas (_P. irritans_) or by bugs (_Cimex_) must be admitted. When more than one case occurred in a house a common source of infection was indicated, such cases occurring simultaneously or within from forty-eight to seventy-two hours after the first. Deratization was the measure mainly relied upon. After an infected house was rat proofed, and the harboring places in the block destroyed, no further cases occurred.