EXAMINATION OF MARINE OBJECTS 101 



be aided considerably by first filling it with some coloured substance 

 to enable its direction to be more easily followed. In fact, the 

 injection of some brightly coloured fluid, forced through the tube 

 by means of a fine-nozzled glass syringe will often enable the course 

 of such a tube to be seen without any dissection at all, the colour 

 of the fluid used being detected through the semi-transparent 

 tissues surrounding it. A mixture of Berlin blue and water, or a 

 mixture of plaster of Paris and water coloured with carmine is well 

 adapted to this purpose ; and if the latter is employed it may be 

 allowed to set, and thus produce a permanent cast from the tube 

 that is being dissected. Perhaps it should be mentioned that if 

 either of the injection mixtures be used for this purpose it must be 

 previously strained through muslin, and that, in the case of the 

 plaster, the mixing and straining should occupy as little time as 

 possible, or it may begin to set before the injection has been 

 completed. 



A very considerable insight into the structure of animals may 

 be frequently obtained by cutting sections through the body with 

 all its organs in situ, but, generally speaking, they are too soft to 

 allow of this without danger of the displacement of those very 

 parts, the relations of which we desire to determine. To avoid 

 this the body should be previously hardened by a somewhat 

 prolonged soaking in methylated spirit, or in a solution of chromic 

 acid prepared as before directed. Then, with the aid of a good 

 razor, very interesting sections may be prepared with the greatest 

 of ease, and the true relations of the various organs throughout 

 the body may be exactly determined by cutting a succession of 

 slices, not necessarily very thin, from end to end, or, transversely, 

 from side to side. 



Even those crustaceans that are protected by a hard, calcareous 

 exo-skeleton, and the molluscs that cannot be removed from their 

 stony shells without injury to their soft structures, may be studied 

 in the manner just described, and this may be done by first 

 soaking them in dilute hydrochloric acid, renewed as often as may 

 be necessary, until all the mineral matter has been dissolved 

 completely, and then hardening the softer tissues in one of the 

 reagents mentioned above. Hydrochloric acid may also be used 

 to dissolve the calcareous shells of foraminifers, the vegetable 

 corallines, and other small forms of life, previous to microscopic 

 examination of the soft parts. 



