19 



and ltd tip inserted into a tube containing a suitable sterile medium. The entire 

 contents of the pipette are now to be expelled by blowing. As an added precaution 

 it is well to break off the tip of the pipette in the culture medium. The blowing 

 may be done by mouth or by a rubber bulb operated either by the hand or by the 

 foot. For continued observation of colony growth, bacteria are isolated on cover 

 slips which are then inverted over depression slides and sealed with a vaseline 

 paraffine mixture. The bottom of the depression slide contains a few drops of 1% 

 agar. This maintains excellent conditions of moisture over a period of several 

 days to several months. Barber 1911 a; 1914. Chambers 1922 a. Kahn 1922,1929. 

 Kahn and Schwarzkopf 1931. Schouten 1905, 1911. Gee and Hunt 1928. 



7. MEASUREMENT OP CAPILLARY PRESSURE. 



A. LMJDIS METHOD 



Landis has adapted the Chambers technique for measuring pressures in small vessels 

 such as capillaries. His microscopic instruments consist of blunt rods and micro- 

 pipettes. The rods are made by fusing small balls 20 u to 50 u in diameter^ on the 

 ends of glass microneedles. Pipettes used vary in diameter from 4 u to 8 u at the 

 tip and are introduced directly into the capillaries. Pipettes and rods are intro- 

 duced into the microscopic field from one side and the pipette is directed downward 

 instead of upward a3 in a hanging-drop preparation. The rods are used to occlude 

 the walls of the vessels and thus stop capillary flow temporarily or permanently 

 by pressure; or to hold the mesentery firmly as the capillary is introduced into 

 the resistant walls of larger vessels. 



The set-up employed is diagrammed below. (Pig. 14) The accompanying description 

 is from Landis. 



The apparatus consists essentially of a reservoir, R, a syringe, S, for exerting 

 large positive or negative pressures, and a column of water, W, by which measured 

 amount of pressure up to 30 cm of water may be applied to the contents of the 

 micropipette. A dye solution may be drawn into the tip of the micropipette by a 

 columnof^nercurv^M^orbycarefull^ 



