216 



SCIENCE 



[N. S. Vol. XXV. No. 632 



But little is known regarding the chemical 

 character of the substances under dispute. 

 The indefinite idea that some toxic sub- 

 stance is produced has been replaced in one 

 or two instances by a definite idea regard- 

 ing the material and its manner of work- 

 ing. Such is the case in hook-worm dis- 

 ease, already discussed, and it may be that 

 more extended study will furnish clearer 

 ideas with regard to other cases. Some ob- 

 servers have determined the substances ob- 

 tained extractively as leueomaines, while in 

 other cases they have been found to be 

 more nearly like enzymes. Certain of them 

 react upon the blood with marked hemo- 

 lytic power, while others of the ferment 

 character afi'ect nerve centers. An alka- 

 loid which arrests muscular action has also 

 been isolated. 



The most difficult case to explain on any 

 other theory than that of the production 

 of toxic principles is the progressive, per- 

 nicious anemia, present in some cases of 

 bothriocephalid infection. In spite of nu- 

 merous investigations the case still remains 

 obscure, but apparently one must admit 

 that at least in special instances this para- 

 site does excrete a particularly active toxin 

 having hemolytic properties. Undoubted- 

 ly, the production of toxins by bacteria 

 leads us to expect similar substances in this 

 case also, but the argument from analogy 

 is a dangerous one in scientific demonstra- 

 tions. Perhaps the strongest argument in 

 favor of the view that parasites produce 

 toxic substances is to be drawn from the 

 occurrence of eosinophilia, which will be 

 considered next. 



Among the white blood cells are such as 

 from the affinity of their granular con- 

 tents for certain stains are known as eosino- 

 phile cells. They constitute from 2 per 

 cent, to 4 per cent, of the normal leucocyte 

 count, and an absolute increase beyond the 

 normal number of 250 per cubic millimeter 

 is designated eosinophilia. The conditions 



which produce an eosinophilia vary so wide- 

 ly that the cells have been termed the most 

 capricious element of the blood. To a cer- 

 tain extent this seems true of the many 

 varied reports of parasitic invasions on 

 record, as some observers in the case of 

 almost every species record the absence of 

 any eosinophilia. Yet evidence is growing 

 that eosinophilia is a strikingly constant 

 symptom of infections with animal para- 

 sites, and experiments on lower animals as 

 well as the most careful and extended ob- 

 servations on man are nearly uniform in 

 their testimony to the existence of abnormal 

 numbers of eosinophile cells in the blood.'' 

 Some authors indicate what may be the 

 explanation of the negative results of other 

 observers. Thus Calvert noted in cases of 

 Filaria Bancrofti that the development of 

 the eosinophilia followed a cyclical course, 

 being more marked when the embiyo round 

 worms are absent from the peripheral blood 

 and decreasing as the embryos increase 

 these. The percentage of eosinophiles 

 varied in one case from 3 per cent, to 15 

 per cent, during twenty-four hours. The 

 observation has been confirmed exactly by 

 Gulland, while other observers record sim- 

 ilar or greater variations, though the mini- 

 mum figures are higher. In fact, such 

 fluctuations seem characteristic not only 

 for this parasite, but also of most other 

 species. In some cases the eosinophilia does 

 not make its appearance at the first of the 

 infection, and after a marked increase sub- 

 sequently declines or even disappears as 

 the disease becomes chronic. A reappear- 

 ance of the eosinophilia and also irregular 

 fliictuations in it during the course of the 



' Thus tapeworm infection, liydatid cysts, the 

 Egyptian blood iiukes, and many other parasites, 

 are associated with an increase in eosinophile 

 cells in the blood. In trichinosis it is the rule 

 and in hook-worm disease the main feature of the 

 blood is an eosinophilia both relative and abso- 

 lute. 



