EXPERIMENTS WITH TAPEWORMS. 3! I 



acid causes them to contract into as dense a mass as possible. 

 This negative response to an inorganic acid is a fundamental 

 and very general characteristic of protoplasm. For example, a 

 very small amount of free acid produces fatal results upon pro- 

 tozoa, developing eggs, spermatozoa, and growing cells in 

 general. "Sour" soils are unfavorable to the growth of most 

 plants. Indeed, this experiment adds one more bit of evidence 

 that one of the primary functions of the acid in the gastric juice 

 is to kill bacteria and other living tissues that reach the stomach. 

 5. Finally these experiments suggest a way in which one may 

 possibly determine why many tapeworms have a specific defini- 

 tive host. Not that they have acquired a particular love for 

 that host, but that the special host furnishes the right stimulus 

 at the right time to call forth the proper reaction in the cysti- 

 cercus. In another paper I have shown that these bladder- 

 worms will not produce tapeworms when fed to pigs, and there 

 is one instance on record where a man swallowed five of them, 

 without harmful results. We shall, no doubt, soon be able to 

 explain much of this peculiar and specific behavior of parasites 

 on the basis of a direct response to favorable or unfavorable 

 physical or chemical stimuli. This will bring some of the little 

 understood phenomena of parasitism into line with the brilliant 

 work that has been done in recent years on the behavior of 

 free-living forms. 



BIBLIOGRAPHY. 

 Braun, M. 



'06 Animal Parasites of Man. 3d Ed. Wm. Wood and Co., New York. 

 Braun, M., and Liihe, M. 



'10 Practical Parasitology. Wm. Wood and Co., New York. 

 Kiichenmeister, F. H. 



'51 Vorlaufige Mittheiling (iiber Cysticercus pisiformis der Kaninchen). Ztschr. 



f. klin. Med., Bresl., V. 2, p. 240. 

 Neumann, L. G. 



'05 Parasites and Parasitic Diseases. 2d Ed. Revised and edited by James 



Macqueen, London. 

 Scott, John W. 



'13 The Viability of Certain Cysticerci in Pigs and in Young Dogs. Science, 

 N. S., Vol. XXXVII. , No. 946. (Abstract.) 



