THE COLLODION BATH. 195 



This stage may be omitted if the objects are of a sufficiently 

 permeable nature, and they may be brought direct from 

 alcohol into the collodion bath. 



299. The Collodion Bath. The next step is to get the objects 

 penetrated with thick collodion. The secret of success here_ 

 is to penetrate them first with thin solutions, then with the 

 definitive thick one. (A thin solution may be taken to mean 

 one containing from 4 to 6 per cent, of dry celloidin ; a thick 

 solution one containing 10 to 12 per cent.) 



If collodion be taken the thin solution may be made by 

 diluting it with ether. If photoxylin or celloidin be taken 

 the solutions are made in a mixture of ether and absolute 

 alcohol in equal parts. Apathy recommends that celloidin be 

 allowed to dry in the air until it becomes yellow, transparent, 

 and of a horny consistency, and that it be then dissolved in 

 the alcohol and ether (sulphuric, free from acid). The solu- 

 tions thus prepared are free from the excess of water that is 

 present in the undried celloidin, and give after hardening a 

 mass that is more transparent and of a better consistency for 

 cutting (Zeit. f. wiss. Mik., vi, 2, 1889, p. 164). 



BUSSE (op. cit., ix, 1, 1892, p. 47) gives the following pro- 

 portions for the successive baths : No. 1, 10 parts by weight 

 of photoxylin or perfectly dried celloidin to 150 parts of the 

 ether and alcohol mixture ; No. 2, 10 parts of photoxylin or 

 celloidin to 105 of the mixture ; No. 3, 10 parts to 80 of the 

 mixture (already used solution may be employed for the first 

 bath). 



The objects ought to remain in the first bath until very 

 thoroughly penetrated; days, even for small objects, weeks 

 or months for large ones (human embryos of from six to 

 twelve weeks, for instance). If the object contain cavities, 

 these should be opened to ensure their being filled by the mass. 



When the object is duly penetrated by the thin solution, or 

 solutions if more than one have been employed, it should be 

 brought into the thickest one. SCHIEFFERDECKER (1. c.) recom- 

 mends that this be done by allowing the thin solution to con- 

 centrate slowly (the stopper of the containing vessel being 

 raised, for instance, by means of a piece of paper placed 

 under it), and making up the loss from evaporation with thick 

 solution. 



