Febkuaby 8, 1907] 



SCIENCE 



213 



the results of parasitism, and though, at- 

 tractive by its very simplicity, no evidence 

 has been elucidated in its support, while at 

 the same time many grounds have been 

 advanced for other views. Accordingly, it 

 is my intention to pass this hypothesis with 

 the mere mention. 



It has been frequently noted that para- 

 sitic infestation tends to retard the devel- 

 opment of the host organism. In fact it 

 does not hinder the general growth of the 

 host strikingly, but arrests primarily its 

 sexual development. This has been espe- 

 cially investigated by Alfred Giard, who 

 denominates the phenomenon parasitic cas- 

 tration and defines it as the sum total of 

 modifications produced by a parasite on the 

 reproductive apparatus of its host, or on 

 the portions of the organism indirectly in 

 relation with that apparatus. The phe- 

 nomenon appears to be wide-spread, in- 

 stances being found in aU branches of the 

 animal kingdom and as the result of the 

 most varied sorts of parasites. The char- 

 acter of this influence becomes evident 

 through a simple comparison. 



When an organ acquires undue impor- 

 tance one of the first physiological results 

 of its hypertrophy is the arrest of sexual 

 reproduction. Similarly when a parasite 

 develops in an organism it causes sterility 

 in its host. Such parasitic castration may 

 be direct or indirect. The first case is met 

 when the parasite destroys directly by 

 mechanical means, or for its nutrition, the 

 genital glands of its host. Parasitic castra- 

 tion is indirect when the producing parasite 

 is not directly in relation with the genital 

 glands, but in some other part of the body 

 of the host. Parasitic castration may also 

 be temporary and then disappear when the 

 parasite is suppressed. 



The modifications caused by parasitic 

 castration affect the genital organs, the 

 secondary sexual characters and the sexual 

 instincts of the infested animals ; it may be 



partial to any degree and may exert the 

 same influences on the secondary sexual 

 characters as age or as artificial castration. 

 Each one of the sexes loses more or less its 

 characteristic attributes and tends to ac- 

 quire in the same degree those of the op- 

 posite sex. Thanks to the effective labors 

 of Professor Giard, this phase of the influ- 

 ence of parasites on the host is more care- 

 fully worked out in comparative fashion 

 than any other in the entire category. 

 However, it would be clearly impossible 

 within the necessary limits of this address 

 to present the mass of evidence which he 

 has collected from all parts of the animal 

 and plant kingdoms. 



A change which is mechanical to a cer- 

 tain extent and yet which has results of far 

 deeper character, is the destruction of tis- 

 sues by such parasites as actually feed 

 upon the cells of the host animal. This is 

 evidently due to the functional activity of 

 the parasite and for that reason will lie 

 outside of the limits of a purely mechan- 

 ical process and may be considered here. 

 Schaper has shown that the liver fluke 

 (Fasciola) feeds upon the substance of the 

 organ in which it lives. Now this destruc- 

 tion of liver tissue removes from functional 

 activity a certain portion of a most impor- 

 tant organ. In addition to that it is fol- 

 lowed by a growth of connective tissue, so 

 that there is a permanent loss in the func- 

 tional activity of the organ. Many differ- 

 ent kinds of alimentary parasites actually 

 feed upon the wall of the canal, with the 

 result that by the feeding and burrowing 

 of the parasites through the mucosa this 

 important structure is destroyed over con- 

 siderable areas ; the wall of the canal comes 

 to be covered with ulcers and suffers at 

 these points permanent functional injury. 

 The serious secondary effects in such cases 

 have already been noted and they are evi- 

 dently not in any sense directly propor- 

 tioned to the extent of the injury, but the 



