182 GARRISON AND LKYNES. 



the shell ouly when exposed to light, we would say that we have repeatedly 

 found from three to five fi'ee-swimming miracidia in one cover-glass 

 preparation from a culture of Paragonimus ova wliicli had been kept in 

 a sealed stone jar and which had been exposed to light only for the 

 fraction of a minute necessary to place a drop of the sediment under the 

 microscope. 



Therefore it Avould appear not only that direct sunliglit is fatal to the 

 life of the ovimi, but that the presence of any light is not necessary to its 

 development, at least to the free-swimming, miracidial stage. 



EFFECT OF SALT SOLUTIONS. 



The ability of the ova of the lung-fluke to develop in salt or brackish 

 water would not be without its important practical bearings. In sea 

 water, taken from Manila Bay, the eggs invariably and rapidly degenerate. 

 Such water contains about 3 per cent of sodium-chloride. In solutions 

 of commercial salt, containing 1.5 per cent or more of the salt, no develop- 

 ment took place. In 1 per cent solutions, from one-third to one-half the 

 ova developed motile miracidia, the others degenerating. In 0.5 per cent 

 solutions the development was nearly as good as in the tap-water controls, 

 though degenerated eggs appeared to be more frequently encountered. 

 In neither the 0.5 or 1 per cent solutions were free-swimming miracidia 

 ever seen. 



DESICCATION. 



Aside from the actual demonstration of the intermediate host and the 

 mode of infection of Paragonimus, there is perhaps no question more 

 important in paragonimiasis than the possibility of the dissemination of 

 the ova in dried sputum or dust. 



As remarked by Stiles, the long retention of the ova in the moist 

 sputum, corresponding to the experimental conditions of Manson, would 

 seldom occur in nature. The natural fate of the ova expectorated in the 

 sputum of the ambulatory paragonimiasis patient (and most such patients 

 are ambulatory) would be either for them to be washed into a body of 

 water or, having been washed free from, or while still retained in the 

 sputum, to become dried on the surface of the ground. It was with a 

 view of determining the probable fate of these ova which become dried 

 that we made a study of experimentally dried ova. 



All ova which were allowed to become dry, even for a few minutes, by 

 evaporation at room temperature, failed to develop thereafter. 



Such a result was surprising in view of the great power of resistance 

 to desiccation shown by the ova of certain other parasites, but repetitions 

 of the test consistently gave the same result. 



In our first tests, the cultures were allowed to remain dry for from one 

 to forty days before the water was renewed. All of ilie ova degenerated, 

 witliout showing signs of development. 



