40 Enshcathed Larvae of some Parasitic Nematodes 



Ancylostoma larvae in suspension on the surface of the pad, giving them 

 two hours in which to bore through the material and get into the skin 

 underneath. I ensured that the blotting paper had good contact with the 

 skin below, and then applied a suspension of active larvae to its upper 

 surface. Immediate examination under the microscope showed the 

 larvae actively wriggling on the blotting-paper. At the end of two hours 

 no larvae were to be seen, and the blotting-paper was removed and put 

 into a drop of distilled water for subsequent examination. The skin just 

 beneath the blotting-paper showed two or three larvae moving on it, 

 but it was impossible to see into the skin because it was too dense and 

 rather pigmented. The preparation Avas placed entire into hot 70 per 

 cent, alcohol, and on the following day the epidermis was split from the 

 dermis and cleared in lactophenol. When mounted on a slide it was 

 found that numerous larvae were embedded in it. 



The water in which the pad of blotting-paper was placed was found 

 to contain numerous empty sheaths. No active larvae emerged from it, 

 thus showing that all had passed through it to the skin. 



I have described these experiments in some detail because they 

 reveal a convenient and easily manageable method of experimentation 

 for skin infection work. 



I next proceeded to use this method with the ensheathed larvae of 

 6r. strigosum and T. relortaefonnis. A young rat, seven days old, was 

 secured and chloroformed. The skin was removed from the abdomen 

 and flanks and was found to be very soft and tender. It was stretched 

 on a sheet of cork and pinned over the hole in the manner already 

 described, and then the cork was floated on normal saline at 37° C. 

 A drop containing numerous active larvae was placed on the surface 

 of the skin, and it was at once evident, on examining the drop under the 

 microscope, that the reaction of these larvae to the temperature of the 

 saline, 37° C, was quite different from that of the Necalor larvae. The 

 latter executed lively downwardly directed movements as though trying 

 to get into the skin, and were decidedly more motile at 37° C. than at 

 laboratory temperature. The G. strigosum and T. retortaeformis larvae, 

 on the other hand, very quickly became sluggish in their movements 

 at the higher temperature. In fact they seemed to be upset and in- 

 commoded by the new conditions and made no downwardly directed 

 movements. The stopper was left out of the jar and the latter was put 

 into the incubator at 37° C. It was taken out at various intervals and 

 the drop, which gradually evaporated, was examined under the micro- 

 scope. It could then be seen that most of the larvae aggregated to 



