200 Transactions of the Society. 



VI. — On Cutting Sections of Sponges and other similar structures with 

 soft and hard tissues. 



By Dr. H. J. Johnston-Lavis, F.G.S., and Dr. G. C. J. Vosmaeb. 



( Head 9th March, 1887.) 



The difficulties that are inTolved in the study of structures where the 

 component tissues have different physical or chemical properties, are such 

 that in some cases the histological or anatomical arrangement has never 

 been thoroughly understood. Perhaps there is no better example of the 

 above difficulties to be found than the Porifera, in which the biologist 

 has to contend with a very complex intermingling of hard and soft sub- 

 stances of entirely different chemical as well as physical properties. We 

 have, in fact, a remarkably delicate protoplasm enwrapping various 

 complicate spicules and granules of siliceous nature. Although many 

 sponges only possess a few spicules, there are others the skeleton of 

 which is so extremely hard that it is utterly impossible to cut through 

 them with the ordinary cutting instruments. It is true sections have 

 been made, even of very hard sponges, but then only relatively small 

 ones can be obtained ; it is, however, an obvious advantage to be able to 

 cut large sections, in order to be better able to study the relation between 

 the canal system and the skeleton. 



Thinking over the mechanical difficulties that thus hinder success, 

 the true solution of the problem is obviously based on a suitable method 

 of equalizing the hardness of the two substances composing a sponge, 

 and which practically consists in rendering the sarcode sufficiently hard 

 and cohesive to withstand the mechanical treatment necessary in cutting 

 the hard siliceous spicules, of retaining all their structure in their relative 

 position, and at the same time not to destroy or even change the histo- 

 logical characters of the most delicate tissue. 



With this object Prof. Sollas has succeeded in making sections 

 through hard siliceous sponges by means of -the freezing microtome. 

 The objections to the method are manifold — the difficulty of keeping the 

 temperature low, and manipulating under such conditions — the com- 

 paratively small increase in the cohesion of the sarcode. 



The method employed by Prof Yon Koch for corals has the great 

 disadvantage of taking too much time if one wishes to make rather large 

 sections ; besides, copal is a substance of which it is difficult to make 

 clear solutions of different strengths. 



Marshall's note about plunging the sponge into boiling Canada 

 balsam shows much of the skeleton and some parts of the canal system, 

 even now and then something of the tissues, but the method is too 

 rough. 



The method we now describe fulfils all the necessary conditions, and 

 is capable of being used with the most delicate stains and of affording 

 complete and entire sections of unlimited size, results almost impossible 

 with soft though tenacious tissues. The only objection that can be urged 

 against our method is that it is somewhat tedious, but in this it has great 



