76 THE PRINCIPLES OF IMMUNOLOGY 



duced, and it is claimed that immunity can be conferred passively. 

 The trypanosomes, however, can become immune to trypanocides. 

 Malarial parasites produce among other things a hemolysin, but 

 there is no indisputable evidence that immunity occurs in malaria, 

 nor have immune reactions been developed. Sarcosporidia of sheep 

 produce a toxin fatal for rabbits in doses of o.oooi gm., against which 

 an antitoxin may be produced in rabbits. Complement-fixation re- 

 action is positive in infested sheep. Man may be infested by the 

 cyst of one tape worm, the tenia echinococcus, the cyst contents 

 being definitely toxic, as shown when a cyst ruptures into a body 

 cavity, e.g., the peritoneum. Serum of infested patients contains a 

 precipitin for the cyst proteins and also a complement-fixing body, 

 Zapelloni reporting 93 per cent, positive complement-fixations in 500 

 cases examined. Of the adult tape worms which infest man the 

 dibothriocephalus latus is the most important from the immunologi- 

 cal standpoint, although this parasite is rare in America. The 

 proglottids contain a thermostabile hemolytic lipoid liberated on 

 the death of the segments by auto-digestion. There is also a ther- 

 molabile hemagglutinin. It is probable that the hemolysin is 

 either associated with other cytolysins or that a species cytolysin is 

 present which also acts as a hemolysin. This is responsible for the 

 primary type of anemia seen in dibothriocephalus latus patients. 

 The serum of these patients contains a precipitin for the fluid ob- 

 tained by antolytic digestion of the segments. Of the nematodes 

 the ascaris, the trichinella spiralis, the hook worm, and certain forms 

 of filaria have been investigated. Certain ascarids produce poison- 

 ous substances without immunological relations. In regard to 

 trichinosis Salzer has found that the serum of recovered patients 

 has distinct therapeutic value in infested patients and protects ani- 

 mals against experimental infestation. Complement-fixation has 

 been found to be of value in the diagnosis of trichinosis. It has been 

 claimed that the anemia of hook-worm infestation is due to a 

 hemolytic poison, but there is doubt that this is as important as 

 the small repeated hemorrhages produced by the bite of these para- 

 sites. There is little of immunological significance in the studies of 

 the filariae. The guinea-worm (filaria medinensis) contains in its 

 body a violent irritant which may be discharged by rupture of the 

 worm during forcible attempts at its removal, and leads to severe 

 local inflammation and even to gangrene. 



Mammalia do not produce poisons except in the somewhat ques- 

 tionable case of the male duck-bill platypus of Australia, a survivor 

 of the very earliest forms of mammalian life. Special glands are 

 said to secrete a poison like that of Australian snakes, which is dis- 

 charged through a hollow movable spur on the hind foot. There is 

 serious question as to the toxic properties of this secretion, certain 

 authorities believing that the sequences of such wounds are due to 

 infection and that the secretion is of importance only as a secondary 

 sex character. The serum of certain mammals is toxic on injection, 



