PART IV. 



GENERAL CONSIDERATIONS REGARDING 

 HISTOLOGICAL METHODS. 



METHODS OF APPLYING RE-AGENTS TO THE 

 TISSUES. 



257. Application of Fluids. Irrigation. When a 

 microscopic object is to be irrigated, a drop of any desirable 

 fluid is placed on the slide close to the margin of the cover- 

 glass, and if necessary a strip of bibulous paper is dipped 

 in the fluid at the opposite side, to remove that which is to 

 be replaced. For the removal of thick fluids such as 

 glycerine, it is necessary to use a pipette (Fig. 45), which 

 may be readily made by blowing a bulb on a glass tube, 

 and drawing one extremity of the tube to a sufficiently fine 

 point. (Read 57, /.) 



258. Application of Vapours and Gases. An ex- 

 ample of a simple method for applying a vapour to a micro- 

 scopic object is given in 89, where the chloroform vapour 

 is applied to cilia. A drop of the fluid is placed on the 

 floor of a glass cell, and the tissue is placed on the 

 under surface of a cover-glass inverted over it. 



For the application of gases, it is necessary to have 

 two tubes in connection with the cavity of a cell : one for 

 the entrance, the other for the exit of the gas. The warm 

 stage, to be presently described (Figs. 48, 49), is so 

 arranged that it may serve as a gas chamber for the attain- 

 ment of this object Various gases, such as carbonic acid, 

 oxygen, etc., may be employed. 



For the production of carbonic acid an apparatus such 

 as that shown in Fig. 46 is convenient. Dilute hydro- 

 chloric acid is placed in a bottle A, and pieces of broken 



