Carmine-stained Pectinatella 179 



to narcotization, so that some very delicate instrument— a hair mounted 

 in a wooden handle is excellent— should be used to test narcotization by 

 pushing the individual polyps. If, on receiving a push, they contract 

 sharply, it is evident that no narcotization at all has taken place, and the 

 amount of menthol that has been sprinkled on the surface should be in- 

 creased greatly. If, on being pushed with a hair, they contract slowly, it 

 is evident that they are partly narcotized. One must be careful not to 

 disturb them further for at least 10 min, for if they contract in a narcotized 

 condition they will not expand again. The right stage for killing has ar- 

 rived when no amount of shoving with a hair will persuade the specimens 

 to contract and an examination under a binocular microscope shows that 

 the ciliary action on the lophophore has not stopped. A rubber tube is 

 used to siphon carefully from the finger bowl enough water so that the 

 remaining layer just covers the specimens. Then the finger bowl is filled 

 with 4 per cent formaldehyde, covered, and put to one side. 



A careful distinction must be made between a "killing" agent, such as 

 formaldehyde, and "hardening" and "fixing" agents. In the present in- 

 stance it is quite unnecessary, since a stain containing in itself an adequate 

 mordant is to be used, to employ any fixative that will combine with the 

 proteins of the specimens, but it is necessary to harden them, in order 

 that they may withstand the treatment to which they will be subjected 

 in staining and dehydration. Four per cent formaldehyde hardens very 

 slowly, and it is suggested that next the specimens be passed to alcohol 

 for the hardening process. 



It is desirable, however, that they be flattened, before hardening, into 

 the shape that they will be required to assume after mounting. It is to 

 be presumed that the purpose of making a microscope slide is to study 

 the object that has been mounted; the depth of focus of microscope lenses 

 is so slight that only relatively thin objects can be studied. It is extraordi- 

 nary how frequently this simple principle is overlooked or how frequently 

 people endeavor to flatten the object after it has been mounted in balsam 

 and is almost invariably so brittle that it will break up during the flatten- 

 ing process. Five minutes' work in arranging the parts before hardening 

 makes all the difference between a first-class and a second-class mount. 

 To arrange and flatten the objects for hardening, the 4 per cent formalde- 

 hyde is replaced with water— a matter of convenience— and then the first 

 specimen to be treated is selected. This specimen is removed to a finger 

 bowl of clean distilled water where it is examined thoroughly to make 

 sure it has no adherent dirt. The object is flattened by hardening it be- 

 tween two slides, but it will be obvious that if it is just pressed between 

 two slides it will be squashed rather than flattened. Anything may be 

 used to hold the two slides apart, although in the present instance a very 

 thick No. 3 or two No. 2 coverslips would give about the right separation. 



