﻿356 The Philippine Journal of Science mu 



ing it with one of known volume. (For methods of estimating 

 the size of hanging drops, see page 342.) The liquid is then 

 drawn into the pipette again. If a definite number of bacteria 

 are to be inoculated, they may first be isolated in a droplet of 

 fluid and the whole droplet inoculated. 



If the substance to be inoculated forms a precipitate with the 

 mercury, a quantity of water or of some indifferent oil, sufficient 

 to separate the substance to be injected from the mercury, may 

 first be drawn into the pipette. 



One should have the cell to be injected well located before 

 filling the pipette and as near to the filling place as possible, 

 so that little time will be lost between charging and injecting. 

 This is the more necessary where it is advisable to keep the pres- 

 sure in the pipette in equilibrium after filling. Lines may be 

 drawn on the cover glass to serve as guides, the cell may be 

 located by means of the vernier on the mechanical stage, or the 

 droplet of the substance to be injected may be placed just in line 

 with the cell so that only one movement of the mechanical stage 

 is necessary in passing from the one to the other. 



The penetration of the plant cells thus far experimented on 

 is easy, if the tip is made fine enough and if the capillary back 

 of it is thick enough to give the pipette the necessary stiffness. 

 If the point of the capillary is too pliable, there may be difficulty 

 in penetrating the cell; if too blunt, there is danger of tearing 

 the cell wall. Sometimes in tough-walled plants there may 

 be some difficulty in piercing the wall without using so much 

 pressure that the pipette, on entering, will penetrate too far. 

 In such cases, one may often obviate the difficulty by pressing 

 the tip against the wall, and then, by moving the mechanical 

 stage gently, bore a hole in the wall. 



In the multinuclear cells of the fungus group Saprolegniaceae 

 and of Nitella and Vaucheria among the algse, the cell wall has 

 been pierced, different substances injected, and the pipette 

 withdrawn with little or no apparent injury to the cells, as 

 judged by the movements of the protoplasm and the subse- 

 quent behavior of the cell. With some mononuclear algae 

 cells, as Spirogyra, the cell appears to be more sensitive to 

 injury. Few animals have thus far been experimented on with 

 the injection apparatus. Mercury has been injected into 

 rotifers, and other substances have been injected into Para- 

 mecium. The larvse of a gnat have been infected with bacteria, 

 and larvse of Stegomyia have been inoculated with defibrinated 



