ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



525 



as to wall in a small chamber with an entrance passage leading into it 

 (fig. 91). 



A drop of blood is allowed to fall into the chamber at A, a coverslip 

 is imposed and gently pressed down with a glass slide, so that as the 

 plasticine is flattened, blood and air are driven out of the passage B, 

 which must be kept patent so that the chamber is completely filled 

 with an even layer of blood (fig. 92). 



The chamber is now incubated at about blood temperature for any 

 length of time, from ten minutes to three or four hours, according to 

 requirements. The whole slide in which the chamber has been pre- 

 pared is immersed in a dish of normal (75 p.c.) saline. During 



Fig. 91. 



Fig. 92. 



incubation the blood clots, the leucocytes escape and adhere firmly in 

 hundreds to the surface of the slide and coverslip which form the floor 

 and roof of the blood-chamber. It is now only necessary to clean away 

 the clot. To do this the coverslip is removed while under the surface 

 of the warm saline by passing beneath it the point of a knife or needle, 

 and what remains of the clot and the plasticine is scraped away with a. 

 small knife. The slide should now be washed in the warm saline until 

 all free red cells have been rinsed off. The slide may now be examined 

 in saline under the warm stage or it may be kept for a time by means 

 of a thin plasticine chamber constructed on a coverslip and filled with 

 saline. 



Jlsculin Bile-salt Media for Water and Milk Analysis.* — F. C. 

 Harrison and J. van der Leek recommend the use of sesculin in media 

 especially when searching for B. coli. iEsculin is a glucoside and 

 undergoes a hydrolytic fermentation when attacked by B. coli and other 

 organisms. It splits into sugar and resculetin, and the latter combines 

 with the iron of the medium to form a dark-brown salt. The reaction 



* Centralbl. Bakt., 2te Abt., xxii. (1909) pp. 547-52. 



