WITH THE MICROSCOPE. 157 



plate upon the stage of the microscope, and allowing one end to pro- 

 ject over the edge so that it may be conveniently heated by a spirit- 

 lamp, any substance may be kept warm upon a glass slide, while 

 subjected to microscopical examination. Max Schultze has recently 

 contrived a brass plate which is fixed by clamps to the stage of the 

 microscope, and extended at the sides so as to form two projecting 

 arms beneath each of which a small spirit-lamp may be placed. A 

 hole is made for the transmission of the light, and close to the place 

 where the slide with the object is situated, is the bulb of a little ther- 

 mometer, the stem of which is so arranged that the degrees can be 

 easily read off. This apparatus has been made by Geissler, of Bonn, 

 fig. 233, pi. XXXVII. In conducting observations upon bodies 

 which are warmed, the loss of fluid from evaporation must be pro- 

 vided against by the use of the moist chamber and immersion lens, 

 or by the little reservoir and conducting thread, pi. XVIII, fig. in*, 

 or by the arrangement described on p. 156. 



Dr. Ransom, of Nottingham, has been long engaged in investi- 

 gations which require the application of heat and cold to the object 

 while under observation. He says, " The mode of using heat for 

 those examinations I have found best so far, is recommended by 

 M. Schultze, only in order to employ with it cold also, I have ordered 

 one to be made of copper instead of brass as the former metal is 

 so much better a conductor, and I trust I shall be able with this new 

 hot stage to preserve an object at any required temperature, and to 

 read off easily the actual temperature which the object has from 30 

 F. to 1 60 F." The principle of this new hot stage is to conduct the 

 heat to or from the object, and not to use currents of air or water. It 

 may be used not only for stimulating movements, but for watching 

 the extremes upwards or downwards, which either arrest them or 

 destroy them. Such a stage must be separated from the microscope 

 by a non-conducting substance. 



Sometime since, I adopted a plan for heating objects by hot air 

 this will be understood by reference to fig. 234, pi. XXXVII, but for 

 most purposes Max Schultze's apparatus is to be preferred. 



Of the Tissues and Organs of the Lower Animals. 



For the most part the tissues of the lower animals may be examined 

 according to the same plans recommended for the demonstration of the 

 structures of the higher classes. In this department, however, the stu- 

 dent will meet with greater variety of texture, and in not a few instances 

 our knowledge of higher structures may be greatly advanced by the 

 careful study of the corresponding tissues in the lowest classes. There 

 are many textures which are peculiar to the lower animals which 



