T. GooDEY 47 



2. A new and easily manipulated method of experimentation for 

 skin infection work is described, in which skin from a young freshly 

 killed animal, rat or mouse, is stretched over a hole in a piece of sheet- 

 cork and pinned in position. The cork is floated on N saline at 37° C. 

 and care is taken to ensure that the saline comes into contact with the 

 underside of the skin. A drop containing the larvae to be tested is 

 placed on the upper surface of the skin. The saline is contained within 

 a suitable glass jar and the whole can be placed on the stage of a bino- 

 cular dissecting microscope and the surface of the skin examined at any 

 moment. 



3. By this method it was found that ensheathed larvae of Neeator 

 amerieanus leave their sheaths and penetrate the skin when the drop 

 of water containing them is allowed to evaporate and become sufficiently 

 shallow to enable them to obtain a purchase against the surface of the 

 drop. These larvae are very actively motile at 37° C. 



4. Ensheathed larvae of G. strigosum and T. retortaeformis do not 

 penetrate the skin under exactly the same experimental conditions. 

 They are not actively motile at 37° C. but become coiled and quiescent 

 at this temperature. Their temperature for optimum activity is shown 

 to be between 22° and 25° C. 



5. Ensheathed larvae of N. amerieanus cannot resist desiccation in 

 air at room temperature and cannot revive on being moistened, whereas 

 the larvae of G. strigosum and T. retortaeformis can withstand air desicca- 

 tion and are easily revived on being remoistened. It is shown that 

 the ensheathed larvae of these two species are more resistant to 

 plasmolysing agents than the ensheathed larvae of N. amerieanus. 



6. The sheath surrounding the larvae in all three species named in 

 the foregoing paragraph is composed of a very resistant substance whose 

 composition is not known. It is not true chitin since it is readily soluble 

 in 5 per cent, caustic soda. 



REFERENCES. 



(1) Bernard, P. H. and Bauche, J. (1914). InfluPiice du mode de penetration 

 cutanee ou buccale du Steithaimrus dentalns, etc. Annales de VInstitut Pasteur, 

 xxvrn, pp. 450^69. 



(2) Brumpt, E. (1921). Mode de penetration do Nematodes dans I'organisme des 

 Mammiferes, histiotropisme et bistiodiagnostic. Comples rendiis des seances de 

 la Societe de Biologie, Lxxxv, pp. 20.3-206. 



(.3) Hall, M. C. (1916). Nematode parasites of Mammals of the orders Rodentia 

 Lagomorpha and Hydracoidea. 



