Fixation and Fixatives 77 



very gently under a stream of warm water: heating over a flame is likely 

 to cause an explosion. 



There is not much use in transferring objects to a vial containing this 

 fluid, for they will fall to the bottom and rapidly exhaust the acid around 

 them. It is much better to hang them with a fine thread of silk from the 

 top of the vial. The decalcification is complete if the object no longer feels 

 hard when pricked with a pin. If there is no part of the object where one 

 may without damage apply the pin, it is very easy to find out if decalcifi- 

 cation is complete by having a dentist or physician observe the specimen 

 on a fluorescent screen by X ray. As soon as decalcification is complete 

 the object should be washed in large volumes of 70 per cent alcohol. 

 Some people claim that phloroglucinol interferes with afterstaining and 

 prefer to restrain the swelling of the tissues with mercuric chloride. The 

 best mixture of this type is: 



McNamara, Murphy, and Gore's Solution: 



Water 80 ml 



95% alcohol 10 ml 



40% formaldehyde 8 ml 



Mercuric chloride 2 g 



Trichloroacetic acid 6 g 



Nitric acid 1 ml 



This is used in exactly the same way as the solution of Haug, but one 

 must, of course, be careful not to handle the object with steel imple - 

 ments because the mercuric chloride will destroy them. 



No really satisfactory method for softening chitinous materials has yet 

 been discovered, although the following is much better than anything 

 else. 



Jurray's Mixture: 



Chloral hydrate 50 g 



Phenol 50 g 



Insects or other chitinous forms are fixed in the fluid of Carnoy and 

 Lebrun and are transferred without washing to Jurray's mixture, where 

 they remain from 12 to 24 hr. Then this mixture is washed out in chloro- 

 form, and the objects are embedded in paraffin. 



Narcotization. There are many small invertebrates that cannot be made 

 satisfactorily into microscope slides after the process of simple fixation. 

 These forms, such as the majority of small hydroids and worms, are con- 

 tractile, so that it is necessary to narcotize them before fixation if they 

 are to resemble the living form after mounting. The whole subject of 

 narcotization is very difficult, for it requires great skill to add slowly small 



