OF MICROSCOPIC OBJECTS. 101 



Some of the large shells are destroyed by this method, 

 but none that are fit for microscopic use. An oblique light 

 shows these objects best. 



These are sometimes treated in the manner described in 

 Chapter III., where the diatoms are spoken of, but many 

 forms are liable to be injured by this severe process. 



It has been before stated that some of the zoophytes may 

 be mounted dry, and others examined as opaque or trans- 

 parent objects according to their substance. They are very 

 interesting when examined in the trough whilst living, but 

 to preserve many of them for future examination they must 

 be mounted in some preservative medium. Sometimes this 

 may be one of the liquids mentioned in Chapter V., but 

 if possible they should be kept in balsam, as there is less 

 danger of injury by accident to this kind of slide. This 

 method of mounting presents some difficulties, but I think 

 that all agree as to the trustworthiness of Dr. Golding 

 Bird's information on the subject, which appeared in the 

 Microscopic Journal. Of this, space forbids me to give more 

 than a condensed account, but I hope to omit nothing of 

 moment to the reader for whom these pages are written. 



After stating that there are few who are not familiar 

 with these exquisite forms, and have not regretted the great 

 loss of beauty they sustain in drying, he informs us that 

 from their so obstinately retaining air in the cells and tubes 

 when dried, it is hardly practicable to get rid of it ; and they 

 also shrivel up very seriously in the process of drying. The 

 following plan, however, he has found almost faultless in 

 their preparation. 



To preserve them with extended tentacles, they should 

 be plunged in cold fresh water, which kills them so quickly 

 that these are not often retracted.* The specimens should 

 be preserved in spirit until there is leisure to prepare them ; 



* It has been stated that the best method of killing zoophytes is to 

 drop alcohol, French brandy, or benzole into th^e salt water in which 

 they are placed ; as this will cause no retraction of tentacles if it be 

 done gradually. 



