CHAPTER IX. 



COLLODION (CELLOIDIN) AND OTHER IMBEDDING METHODS. 



150. Advantages of the Collodion or Celloidin Method. Collo- 

 dion (or celloidin) masses do not require the employment of 

 heat. They do not require that the objects should be cleared 

 before imbedding, and that is an advantage in the case of 

 very large objects. They are more or less transparent, 

 which facilitates the orientation of the object. And they 

 are specially indicated for very large objects, for the soaking 

 in collodion being quite inoffensive to the most delicate ele- 

 ments may be prolonged if necessary for weeks, thus ensuring 

 the harmless penetration of objects that would be literally 

 cooked if they were submitted to a paraffin bath of like 

 duration. Lastly, the mass being quite transparent after 

 mounting, it is not necessary to remove it from the sections 

 before staining and mounting them ; it may remain, and 

 fulfil the function of an admirable support to the tissues, 

 holding in their places brittle or detached elements that 

 without that help would fall to pieces and be lost. 



There are two disadvantages. One is that the process is 

 a very long one ; as usually practised, the collodion process 

 requires some three days for the imbedding of an object that 

 can be imbedded in paraffin in an hour (though the time 

 may be greatly abridged by GILSON'S rapid process given 

 below). Another is that it is impossible to obtain with 

 celloidin sections as thin as those furnished by paraffin ; the 

 lowest limit I have been able to attain to is 7 /n, which for 

 some work is not sufficient. Other workers seem to have 

 obtained thinner ones ; but at any rate this cannot be done 

 without difficulty. 



As to the choice of a process, I urgently recommend the 



