ON THE SPALTEHOLZ METHOD OF PREPARATION. 



335 



sources for identification ; in two instances the senders spoke of 

 their being in numbers when found. 



Phryganea grandiosa, 

 the largest of our Caddis-flies, when in the larval state forms its 

 case from segments of the hollow stems of aquatic plants, then 

 protects each joint by adding a frill composed of leaf -lobes from 

 the Horn wort. To do this the larva climbs a plant, and forces 

 itself into the top whorl, head downwards : then, when the leaf- 

 lobes close round it, cuts them off and glues each singly on the 

 case, the loose ends pointing backwards. 



Mr. C. Tate Regan, M.A., F.R.S., F.Z.S., described the present 

 state of knowledge regarding the life-history of the Common Eel, 

 illustrating his remarks with lantern-slides. 



November 6th, 1917. 



Dr. A. Smith Woodward, F.RS., Vice-President, 



in the Chair. 



The Spalteholz Method of Preparation. 



Mr. R. H. Burne exhibited a Common Frog prepared by the 

 method of Dr. Spalteholz, in which the highly elaborate saccus 

 endolymphaticus of the internal ear was very clearly shown. 



The method of preparation in question was introduced in 1906 

 by Dr. Spalteholz of Leipzig, and was subsequently brought by 

 him to very considerable perfection. Its aim is to render the 

 tissues of an organ or even of an entire small animal trans- 

 parent. 



The specimen is first thoroughly dehydrated and then fully 

 permeated by a mixture of oils of refractive index as nearly as 

 possible the same as that of the dehydrated tissue. 



It will be noticed that the method is quite similar to that 

 employed by the microscopist in clearing sections or small objects 

 for examination by transmitted light. Its success when applied 

 to gross objects depends on the degree of accuracy with which 

 the refractive index of the clearing agent is adjusted to that of 

 the tissues to be rendered transparent. With a clearing agent 

 accurately compounded the results are often very brilliant and 

 of considerable value for research or museum purposes. This is 

 especially the case with complex organs or whole animals owing 

 to the fact that different tissues have slightly different indices of 

 refraction, so that in the finished preparation the whole object is 

 not uniformly transparent, but the several parts appear in it as 

 filmy shades of various opacity. 



