208 



SCIENCE 



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



appendicitis since their presence in this 

 organ constitutes a pathological rarity.^ 



Evidently in producing ulcerations of 

 the intestinal mucosa parasites facilitate 

 the absorption of toxins from the canal and 

 permit the inoculation of this layer with 

 pathogenic bacteria from the intestinal con- 

 tents. They can thus be the agents of 

 inoculation for numerous diseases. Guiart, 

 who defends this view most strongly, be- 

 lieves that intestinal parasites play an im- 

 portant role in the etiology of diseases of 

 the intestine and liver, such as insects play 

 in the etiology of blood infections. He ad^ 

 vances evidence to support the view from 

 the records of both human and comparative 

 parasitology. While recognizing fully that 

 the infections are bacterial, he emphasizes 

 the necessity of some inoculating agent as 

 in a sense the most important element, since 

 pathogenic bacteria are generally present 

 in the alimentary canal. No one can 

 doubt, he maintains, that Eberth's bacillus 

 is the agent of typhoid fever, but there is 

 reason for regarding it as innocuous if the 

 intestine is undamaged. In a population 

 drinking contaminated water only a few 

 X^ersons in reality are infected. Any intes- 

 tinal parasite capable of inflicting a wound 

 may infect the host if the bacillus is pres- 

 ent. The infecting agent may be an 

 Ascarid, a hook worm, a fly larva; most 

 commonly Guiart believes it to be the whip 

 worm (Trichuris) which bores into the 



' Galli-Valerio has subjected a recent fatal ease 

 of appendicitis to most careful examination and 

 finds in the contents of the perforated appendix 

 numbers of Oxyurias vermicularis and eggs of 

 Trichuris, while sections demonstrated numerous 

 perforations of the mucosa made apparently by the 

 parasites and in one case the worm still within 

 the tissue. Neither the presence of the parasites 

 nor the evidences of their work could have been 

 determined without a microscopic examination, 

 and in view of the usual lack of such examination 

 this is sufficient answer to the objections cited 

 above to the probable role of parasites in the eti- 

 ology of this disease. 



folds of the intestinal mucosa with its 

 attenuated anterior end. This parasite 

 Guiart calls the lancet of inoculation and 

 demonstrated its presence in eleven out of 

 twelve typhoid cases in one group. It is 

 interesting to note that in 1762 this species 

 was looked upon as the cause of typhoid 

 and its abundant presence was noted in 

 many epidemics by early investigators. 

 After having gone to the opposite extreme, 

 scientific opinion now shows a tendency to 

 return to its earlier position and to regard 

 the parasite an active factor in the intro- 

 duction of the disease. 



This unfortunate function as introducers 

 of bacteria is, however, not confined to in- 

 testinal parasites. The chigo, or ' jigger, ' a 

 sand flea of some tropical regions, which 

 burrows into the feet of natives, renders its 

 host thereby exceedingly liable to infection, 

 which in its secondary effects in the tropical 

 clime, makes of a trivial injury one of 

 serious consequence. The guinea worm, 

 M'hich burrows through connective tissue, 

 approaching the surface at the time when 

 it desires to deposit its embryos and pro- 

 ducing there small ulcers or openings to 

 the exterior, menaces the well being of its 

 host, not by virtue of its own activity, but 

 through the chance for infection to which 

 it has subjected the host. 



Parasites in many cases produce mor- 

 phological or structural changes in their 

 hosts, which may be classed in general as 

 progressive histological changes in that 

 they lead to the accumulation of material 

 through the mi;ltiplying of the host cells. 



Billroth indicated the extremely im- 

 portant fact that the miiltiplication of 

 epithelial cells is caused by infection with 

 micro-organisms and it has been shown that 

 protozoa as well as bacteria may cause in- 

 fected cells to multiply. Thelohan has 

 shown that myxobolid infection produces 

 a proliferation of muscle cells. Hofer and 

 Doflein ascertained that in kidney infec- 



