380 DR. PRITCHARD. 



Methods of preparing the Cochlea for Microscopical 

 Investigation. By Urban Pritchard, M.D., Demon- 

 strator of Physiology, King's College, London. 



When I undertook the inv^estigation of the cochlea, at 

 the suggestion of Professor Rutherford, I Avas totally unac- 

 quainted with the method of preserving, softening, and 

 cutting its structures, and were I to enumerate the experi- 

 ments I made, the valuable cochleae I spoilt, and the failures 

 I experienced before obtaining any results, I should fill 

 many pages, and only succeed in wearying the reader by the 

 monotomy of my disappointments. I shall therefore confine 

 myself to describing the methods which at last proved suc- 

 cessful, merely alluding to the chief points of the fruitless 

 attemjits. 



First, then, the lamina spiralis of the cochlea may be 

 examined in its fresh state, either as it is or stained by 

 means of carmine, aniline blue, &c. For this purpose I 

 found that the cochleae of new-born animals, as kittens, the 

 most readily worked, for in them ossification has not pro- 

 ceeded far, and yet the organ is nearly, if not quite, as large 

 as in the adult animals. 



But the specimens thus obtained are not of much value 

 for showing the rods or any of the parts in sitii ; hoAvever, I 

 have one or two pretty preparations of the nerve-cells of the 

 ganglion of the lamina spiralis, and also of the membrana 

 basilaris. 



Of course no vertical sections can be obtained from the 

 tissue in a perfectly fresh state, and as these are far more 

 instructive than the flat preparations of the lamina some 

 method of preparation becomes necessary. 



The processes consist in hardening the membranes, soften- 

 ing the bone, cutting, staining, and mounting the sections. 



Hardening the soft structures. — For this j)urpose a solution 

 of chromic acid from a half to a quarter per cent. I have 

 found most successful, and the tissue may be allowed to soak 

 in this fluid for tAvo or three months, or cA^en more ; but I 

 have obtained better results by only alloAving it to remain in 

 the solution for tAvo or three Aveeks. HoAA'ever, I think that 

 both the longer and shorter periods have their distinct advan- 

 tages, as I fancy that some of the cells are all the better for the 

 longer maceration. I have also obtained A^ery good results 

 from using Miiller's fluid for hardening the membranes, <S:c. 



Perosmic acid did not appear to me to be of any service. 



