PREPARING COCHLEA FOR MiCROSCOPICAL INVESTIGATION. 381 



but tliat may be because I did not use it properly ; however, 

 I should not recommend it. 



Softening the bone. — This Avas one of my greatest difficul- 

 ties, and I spoilt many valuable cochleae before I arrived at 

 the right strength of acid to use. Nitric or hydrochloric acid 

 may be used ; I prefer the former, and have found half to 

 one per cent, the best strength. But the exact strength and 

 time required must, of course, depend on the cochlea taken. 

 Thus, a kitten's cochlea will soften in less than twenty-four 

 hours in a half per cent., a cat's or dog's in three or four 

 days, while the human cochlea well cut down requires nearly 

 three weeks in a one per cent, solution. In softening the 

 thicker and harder bones it is very important to use a large 

 quantity of the solution, or to change it frequently, otherwise 

 it may take months to soften. 



The bone may be softened by the chromic acid tilone if 

 there be not much earthy matter to dissolve. 



The softening acid should be added to the chromic acid 

 solution during the latter days or weeks of the maceration, 

 as the hardness of the bone requires. 



Cutting the sections. — By the preceding processes the bony 

 tissue is rendered quite soft, and the membranous tissue 

 sufficiently hard. But on attempting to make sections 

 another difficulty arises — the Avhole tissue gives way before 

 the knife or razor, making it almost impossible to obtain a 

 satisfactory slice, and, moreover, the membranes being un- 

 supported, they are inevitably torn and destroyed. 



Dr. Hensen recommends Bottcher's plan of injecting the 

 cochlea with a hot solution of gelatine, which on cooling 

 gives a very good support to the membranes. To this 

 method, however, there are two very serious objections. 

 First, it renders the whole cochlea still softer, and secondly, 

 the jelly is apt to contract and drag the membranes asunder. 

 For these reasons I was unable to make any satisfactory 

 sections either by hand or by means of Stirling's machine. 



At last I tried the following plan, which proved successful, 

 both for supporting the membranes and rendering the tissue 

 sufficiently tough tor making thin sections. I can fully re- 

 commend [it to any one who may be carrying on similar 

 researches on the cochlea, not only on account of the satis- 

 factory results obtained, but also on account of its simplicity 

 and the focility Avith which it may be worked. 



Place the softened cochlea (taken directly from the acid 

 solution) in a small conical bag of paper filled with a strong 

 solution of gum arable ; allow it to soak for an hour or two, 

 then put the bag into absolute alcohol, and set aside for 



