Nov. 2s, 1918 Observations and Experiments on Intestinal Trichince 477 



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Fig. 2. — Trichina spi- 

 ralis: Outline draw- 

 ing of a larva in the 

 act of molting out- 

 side of the host. 



DWARFS PRODUCED IN CULTURE DISHES 



In the course of the observations on the molting of the larvse in cul- 

 ture dishes it was found that sometimes after the first molt the parasite 

 is only a little more than one-half the size of the unmolted lar\^a (fig. 

 1,3). These dwarfs maintain their vitality for some time after the 

 molt, although they appear to be exceedingly sluggish. 

 Their tissues, too, are not as transparent as the tissues 

 of normal larva; after the first molt. In fact the 

 worm as a whole is darker in color and presents a 

 very compact appearance. It is possible that the 

 decrease in size is a result of food deprivation in- 

 volved in the removal of the parasites from their nor- 

 mal environment to a culture dish. It is rather 

 remarkable that under such conditions a second nrolt 

 should be initiated almost immediately after the 

 casting off of the first cuticle. The outline of the worm shown in figure 

 3 is of a dwarf larva of Trichinella spiralis in the course of the second 

 molt. The parasite was obtained 18 hours after artificial infection, 

 and the observation was made about 4 hours after the worm had been 

 kept at room temperature. 



CHANGE IN RESISTANCE OF INTESTINAL TRICHINAE 



A number of investigators have been struck by the marked powers of 

 the intact larvae to resist various unfavorable conditions. Davaine (j) 



states that he kept larvae isolated 

 from the muscles alive in fresh water 

 for a month. The same writer also 

 notes that after having reached the 

 adult stage in the intestine this re- 

 sistance is lost, and that the worm^s 

 perish in fresh water within one hour. 

 The present writer has observed 

 that the decapsuled larvae are very 

 tolerant to distilled water, concen- 

 trated sodium-chlorid solutions, weak 

 solutions of alcohol (35 per cent), 

 potassium cyanid, acids, and many 

 other toxic agents. After the first molt as well as after subsequent molts, 

 and to a lesser extent while the molt is in progress, the tolerance of the 

 larvae is suddenly reversed and is replaced by a marked sensitiveness. 

 Distilled water is highly toxic to them and brings about their death in a 

 few minutes. The parasites have lost their tolerance for acid, and suc- 

 cumb very rapidly to very weak dilutions (999 cc. of water and i cc. of 

 hydrochloric acid, sp. gr. 1.19) This marked sensitiveness character- 



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Fig. 3. — Trichina spiralis: Outline drawing of a 

 dwarf larva after the first molt outside of the 

 host. The beginning of the second molt is 

 indicated. 



