192 ANNIE PORTER. 



blue and neutral red were occasionally used as intra-vitam 

 stains and were sometimes useful. 



For fresh preparations used in work on hereditary infection, 

 the ovaries and gut were dissected out very carefully, kept 

 as far as possible relatively in situ, and mounted in 0'75 per 

 cent. NaCl solution. The behaviour of the Crithidia visible 

 through the walls of the gut and tlieir action when they 

 passed out from it were then most carefully watched. 



I have attached very great importance to the study of the 

 living organism in all its phases. 



For making permanent preparations the alimentary tract 

 of the Dipteran host was carefully removed and divided into 

 portions as before. These isolated portions were usually 

 teased very finely and fixed wet. Formalin vapour and osmic 

 acid vapour were chiefly used for instantaneous fixation of the 

 hanging-drop preparations, which were then spread. The 

 preparations were subsequently treated with methyl or ethyl 

 alcohol. Corrosive-acetic-alcohol (Schaudinn's fluid) and 

 Bouin's fluid (slightly modified and containing a little alcohol) 

 were also used for fixation. 



Various stains were employed. Giemsa's stain gave some 

 pretty results; thionin acted rapidly and well; iron-haema- 

 toxylin, carefully differentiated Avith iron-alum, was very 

 serviceable ; while gentian violet and Delafield's htematoxylin 

 were of great use, particularly in obtaining details of the 

 membrane and flagellum. 



In the investigation of Crithidia melophagia, as in all 

 other flagellates on which I have worked, I found that pre- 

 parations mounted in neutral Canada balsam were superior 

 to dry films or to films mounted in any other media. 



Preparations of ovaries, eggs, and puparia were treated 

 similarly. Special methods adopted are detailed in the section 

 dealing with hereditary infection (p. 204). 



DiSTEIBUTION OF THE PaEASITE IN THE HoST. 



The Crithidia parasitic in the alimentary canal of Melo- 

 phagus are often mixed with the blood obtained by the ked 



