248 The Microscope. 



(Sponges, Equisetums, etc.) in a dilute solution of fluoric acid, 

 fluoride of ammonium. Only rubber or guttapercha vessels 

 should be used for the bath, and exceeding care must be taken 

 lest the fumes be inhaled or any fluid spilled on the hands, as it 

 is a most corrosive poison. 



IODINE. 



A excellent reagent for the study of the central nervous 

 system and ganglia is made as follows : 



Iodide of potassium 6 grammes. 



Iodine 4 grammes. 



Water 100 cc. 



If for any particular specimen the above solution is found 

 too strong (e. g. if the outer parts are too deeply colored while 

 the inner portions are but slightly acted upon), it may be freely 

 diluted with water. After saturation the preparation should be 

 hardened in alcohol in the usual manner. No staining is neces- 

 sary as that has already been accomplished by the iodine, 

 though for pathological study, especially with cancerous tissues, 

 a slight staining with picro-carmine is advantageous. 



HOT WATER. 



In many instances, (e. g. insect and anstaceum eggs), a firm 

 covering membrane so resists the action of reagents as ordinar- 

 ily applied, that maceration takes place before the fluid has 

 fully penetrated, and the specimen is ruined. In these cases 

 recourse may be had to hot water or a two per cent, salt solu- 

 tion ; it should be of a temperature not to exceed 80°-90° c, as 

 the albumens of low organisms coagulate at a lower tempera- 

 ture than those of higher forms. It should be used but for a 

 few minutes, and the egg hardened in the usual way with alco- 

 hol, beginning with 50 per cent, and finishing with 96 per cent. 

 Of course the usual killing fluids might be used in the same 

 way, but it is frequently impossible to fully extract them 

 through the embryonic membranes and consistent integuments 

 of many of the lower orders of life. Except in these cases hot 

 water is of little service and but seldom used. Even in these 

 cases it might better be replaced by 



