154 WHAT IS A PLANT? 



Owing to the large amount of balsam contained in the cell, 

 the slide, whilst in this state, requires to be handled very carefully, 

 and must be kept in a horizontal position. A good body of some 

 cement is therefore necessary to protect it and to give rigidity to 

 the whole. I have found, after many trials, that the best plan is 

 to give two coats of Ward's brown cement, leaving the slide 

 several hours to dry before applying the second coat. Next put 

 around the cell a good body of the following cement : — Red lead, 

 w^hite lead, and litharge, each in powder, mixed together in boiled 

 linseed oil, with a palette-knife, and put on with a penknife in the 

 same way as putty would be used. This cement will take a week 

 to harden, when it must be pared smooth, and finished off with 

 black varnish. It is important to remember that the process 

 cannot be hurried. It is, however, quite easy to do several speci- 

 mens at one time, and whilst some are in one part of the process 

 others are passing through other stages, so that it seems far longer 

 and more complicated than it really is. Insects prepared by this 

 method show the whole of the internal organs in their proper 

 position, and when examined with the spot-lens illumination, the 

 whole of the tracheal system will be very plainly visible. They 

 also polarise brilliantly. This is probably owing to the action of 

 the acid in the bleaching solution on the different tissues. 



Mbat is a DMant ? 



By H. W. S. Worsley-Benison, F.L.S., 



Lecturer on Botany at Westminster Hospital, President of the 



Highbury Microscopical and Scientific Society. 



Part II. 



VII. — Function of Circulation. 



THE presence of circulatory organs formed Cuvier's second 

 distijidion. Animals, possessing a digestive cavity, taking 

 various foods into it which needed sundry operations to be 

 performed on them, and requiring to be quite independent of the 



