142 



ANIMAL PARASITES. 



the enormous fertility of the parasites, even a moderate number may give rise to a 

 severe infection. 



For the minute examination of the parasite, bits of muscle should be hardened in 

 Orth's fluid and alcohol, decalcified if necessary, and, after embedding in celloidin, thin 

 sections cut and stained double with hsenmtoxylin and eosin, and mounted in balsam 

 Bits of muscle may be also teased, the embryos picked out with a needle, and the cysts 

 either broken open under a lens with the needle, or squeezed under the cover glass. 

 The embryo worm thus set free may be mounted in a mixture of equal parts of glycerin 

 and picric acid. The adult forms, which may be obtained by feeding rabbits with un- 

 cooked trichinous muscle, and examining after the proper interval, may be hardened in 

 Orth's fluid, and mounted in a mixture of equal parts of picric acid and glycerin, or 

 in the same mixture which has been lightly tinged with eosin. 



Arthropods. 



The scope of this work does not permit us to enter in detail into the 

 subject of external parasites, which will be found described in treatises 

 on diseases of the skin or in the general works on 

 parasites referred to below. But, owing to their 

 frequent occurrence and practical importance, we 

 may briefly describe two of the 

 more common forms of arthro- 

 pods, the "itch insect" and the 

 "louse." 



The common "itch insect" 

 Sarcoptes hominis (Acarus 

 scabiei) is shaped somewhat 

 like a turtle, with a chitinous 

 covering, and presents the gen- 

 eral appearance seen in Fig. 

 69. The female is about 0.45 

 mm. long, the male a little 

 smaller. 



The parasite bores little tunnels in the skin, in which the eggs are laid 

 and the young hatched. After a few days these bore fresh channels in 

 the skin. For their detection a bit of the superficial layer of the skin is 

 snipped out with curved scissors, dehydrated and cleared up with oil of 

 cloves, and examined under a low power, when the tunnels and the para- 

 sites, if present, will be readily visible. 



The head louse, Pediculus capitis, is from 1 to 2 mm. long, the female 

 being slightly the larger. The general appearance of the insect is seen 

 in Fig. 70. ' 



Method of Study of Insects. 



These, if small, may be cleared in turpentine and mounted in balsam, or sections 

 may be cut after embedding in paraffin. 



1 Bibliography. Especially to be recommended for detailed description of human 

 and animal parasites is the small work of Moniez, "Traite de Parasitologie, " Paris, 1896. 



Consult also, especially for the forms of eggs and other parts of animal parasites 

 which may be found in the excreta, ron JakscJi, Wood, or Simon, or other works on clini- 

 cal microscopy. 



The Reports of the Bureau of Animal Industry of the U. S. Department of Agri- 

 culture contain many valuable data relating to animal parasites and the diseases of 

 animals in the United States. 



FIG. 69. SARCOPTES HOMINIS 

 THE "ITCH INSECT." 



Female ; back view. 

 Furstenberg. 



After 



FIG. 70. PEDICCLUS 

 CAPITIS THE "HEAD 



LOUSE." 



Male. After Braun. 



