CHAPTER V 

 CHEMISTRY OF THE ANIMAL PARASITES^ 



This subject has received much less consideration than its import- 

 ance deserves, and we are quite in the dark as to how much of the 

 effects produced by animal parasites are not merely mechanical, but 

 are due to soluble poisons that they maj^ secrete or excrete. Some of 

 the parasites probably cause harm mechanically and in no other way, 

 but with most of them there is more or less evidence of the forma- 

 tion of poisonous substances. The composition of the bodies of the 

 animal parasites is an almost unexplored field, but we have no reason 

 to believe that the composition of the cells of invertebrates differs 

 essentially from that of the cells of higher organisms. Perhaps the 

 most characteristic constituent observed in many forms is chitin, which 

 forms a large part of the outer covering of the encysted forms, and 

 probably of many of the worms. Glycogen is usually abundant in 

 the invertebrates, and the animal parasites form no exception, ^ this 

 carbohydrate having been found in their bodies bj^ many observers. 



Eosinophilia. — One of the most characteristic features of the animal parasites 

 is that they exert a positive chemotaxis for eosinophile leucocytes.^ 



An increase in the number of these cells in the blood, as well as a local accum- 

 ulation in the tissues nearest the parasite, has been observed in infection with prac- 

 tically all the animal parasites.'' Of these, infection with TrichineUa spiralis 

 causes the most pronounced eosmophilia, presumably because of the great number 

 of parasites present in the tissues at once. That the eosinophilia is due to the 

 action of the soluble products or constituents of the parasites has been shown by 

 experimental injection into animals of extracts from the bodies of the parasites. 

 Calarnida has found that extracts of do^ tapeworms also, when placed in the tissues 

 in a capillary tube, cause an accumulation of eosinophile cells in the tube.^ 

 Experimental infection with excessive numbers of trichinclla causes a rapid diminu- 

 tion in the number of eosinoi)hile leucocytes, which also show evidences of disinteg- 

 ration in the bone-marrow and lyin])h-glands. Such large injections are fatal, 

 which suggests that the eosinoiihilia has a jirotective influence. In favor of this 

 view is the observation of Milian," who foiunl that sarcosporidia in l)cef are des- 

 troyed bj^ a violent leucocytic reaction, the prevailing cell be'ng the eosinoi^hile. 

 As the eosinoi)hUe increase does not occur until several days after the infected 

 flesh is eaten, the chemotactic substance is not lilterated from the encapsulated 



1 General references to this subject will be found in v. Fiirth's '' Vergleichende 

 chemische Physiologic der nioderen Tiere," .Icna, 1903; Faust's ''Tierische Gifte," 

 Braunschweig, 1900; Koch, Krgebnisse Pathol.. 1910 (XIV(l)), 41. 



2 See Pfliiger, Pfliigers Arch., 1903 (9{)), 1.'d3. 



■'Literature by Opie. Amer. Jour. Med. Sci., 1904 (127), 477; Stiiubli, Deut. 

 Arch. klin. Med., 1900 (85), 280; Iliibner, ibid., 1911 (104), 280; Schwarz, Ergcb. 

 allg. I'athol., 1914 (17,), 138. 



' LiteratiM-e by Bruns, Liefmann and Miickel, IMiincli. med. Woch., 1905 (52), 

 253; Vallillo, Arcli. wiss. u. prakt. Tierhk., 1908 (34), 505. 



' Negative rcsult.s were olUnincd with extracts of Sclcrosloma equinum by 

 Gro.s.so (Folia Ileinatol., 1912 (11), IS). 



• Hull, et Mem. Soc. Anat., 1901 (.Sor. (i, T. 3), 323. 



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