Febbuabt 8, 1907] 



SCIENCE 



215 



dangerous than the former; and yet it 

 should be remembered that our precise 

 knowledge of these matters is exceedingly 

 limited. The production of a substance by 

 extraction from a parasite is not sufficient 

 evidence that the animal actually elimi- 

 nates this material. It may be that in the 

 final step of elimination there are changes 

 which radically alter the character of the 

 substance, and that consequently there is 

 under natural conditions no such material 

 in position to act upon the host individual. 

 It should also be remembered in this con- 

 nection that the parasites are generally lo- 

 cated in those organs into which waste is 

 normally eliminated and by which it is dis- 

 charged from the body; and, furthermore, 

 that the parasitic organism sets free but a 

 small amount of such waste material at any 

 one time. These conditions would appear 

 to indicate a minimum effect upon the host, 

 if, indeed, any such existed. 



On the other side, there are also certain 

 incontestable facts. Not only is the re- 

 covery of such toxic substances from para- 

 sitic organisms by chemical means un- 

 doubted, but also it is known that as a re- 

 sult of injury or surgical intervention when 

 a hydatid cyst is ruptured and the liquid 

 content is diffused through the body, there 

 are absorbed from it toxic substances which 

 provoke serious results. Normally, the 

 bladder worm is surrounded by a cuticula 

 which retards osmosis, so that only a negli- 

 gible quantity of toxin can be dispersed, 

 while the rest is accumulated in the vesicle. 



Another argument which has been ad- 

 vanced to question the actual relation of 

 these toxic substances to the pathological 

 conditions of the host is the great amount 

 of variability in different eases, not only 

 as between the effect of different parasites 

 which would naturally be explained on the 

 basis of different types of toxic substance, 

 but also with regard to the effect of the 

 same parasite in different cases. Now this 



may easily be due to individual suscepti- 

 bility on the part of the host animal, but 

 there is another feature which would go 

 far towards explaining this variable effect 

 and yet it has never been suggested in this 

 connection. Under certain conditions an 

 animal will absorb toxic substances from 

 its own alimentary canal and induce dis- 

 eased conditions within itself as a result of 

 this perverted function. The application 

 of the same principle to the case of para- 

 sites would account for the absorption of 

 toxic materials by one host and their elim- 

 ination in another case. 



So far as the protozoa are concerned, 

 the evidence is positive that in some cases 

 toxic materials are the cause of the eft'ect 

 produced by the parasite. Thus the Hemo- 

 sporidia of malaria undergo their develop- 

 ment within the red blood corpuscles, and 

 at the time of breaking up into spores the 

 corpuscle is destroyed and the accumulated 

 toxic material set free in the blood. Since 

 the phenomena are synchronous for a large 

 number of the parasites the amount of 

 toxic material set free at once is consider- 

 able and is followed immediately by a 

 febrile reaction, the periodicity of which is 

 related to the successive reproductive cycles 

 of the parasite. 



The case of the Trypanosomes which are 

 the cause of sleeping sickness is less defi- 

 nitely demonstrated, but apparently of the 

 same type. In this disease no pathogenic 

 changes can be observed in the host save a 

 slight inflammation of the vascular mem- 

 branes surrounding the spinal cord and 

 brain. The toxins which the organisms in 

 the spinal fluid produce must be set free 

 in this fluid and thus act directly upon the 

 central nervous system with the lethal 

 effect characteristic of the disease. The 

 result here is certainly not morphological 

 and is satisfactorily explained on the basis 

 of the production of a deleterious chemical 

 stimulation. 



