156 HOW TO WORK 



and transmitted light under high powers, with the aid of the binocular, 

 p. ii. 



249. Of keeping Bodies moist while under microscopical Obser- 

 vations. In order to study the changes occurring during the growth 

 and multiplication of some of the simplest organisms which live in 

 water, it is necessary to adopt some plan for preventing, or compen- 

 sating for, the evaporation which takes place. This may be effected, 

 as recommended by Recklinghausen, by adapting a piece of sheet 

 India-rubber tubing to the glass ring fixed on an ordinary glass slide, 

 the diameter of the ring being sufficient to allow a piece of thin glass 

 to be placed within its circumference. The upper end of the tube is 

 tied round the object glass of the microscope. Thus a moist chamber 

 is made, and if one of Hartnack's " immersion lenses " be employed, 

 observations may be continued upon a given object for some time. 

 The moist chamber is, however, better adapted for use with low 

 than with very high magnifying powers. See pi. XXXVI, fig. 232. 



I have found that the same object is gained if the loss of fluid by 

 evaporation is compensated for by a little reservoir of water, fixed at 

 one end of the slide, from which a small piece of blotting paper or 

 silk thread conducts the fluid to the object as fast as evaporation 

 takes place. By placing a little cement round two thirds of the thin 

 glass cover, sufficient space is allowed for the requisite access of air, 

 while at the same time loss by evaporation is reduced to the smallest 

 amount. By this arrangement the growth of the spongioles of plants 

 can be studied very successfully. 



A small quantity of fluid or semi-solid matter containing various 

 kinds of living matter, may be preserved for some days without the 

 death of the living matter it contains taking place, by the following 

 arrangement. A small glass tube about half an inch in diameter 

 and an inch and a half in length is prepared, the edge of one 

 extremity being turned outwards in the blow-pipe flame, so that 

 very thin membrane may be tied over it. The tube is so arranged 

 that the membrane just touches the surface of some distilled water 

 in a small dish or capsule. The whole may be placed in a hot-air oven 

 maintained at a temperature of 100 F. In this way I was enabled 

 to keep living matter freely exposed to the air, whilst evaporation was 

 compensated for by the gradual imbibition of fluid from below 

 through the pores of the membrane. I have succeeded in preserving 

 masses of germinal matters from the higher organisms alive for a 

 considerable time longer than they would have lived at the ordinary 

 temperature of the air. 



250. Of Keeping Bodies at a Uniform Temperature higher than 

 the Air, while under Microscopical Observation. By placing a brass 



