DIGESTION OF SPONGE. 103 



The same process precisely is called out in the absorption 

 of the catgut ligature, which is progressively invaded by leu- 

 cocytes, which digest the foreign substance and remove it by 

 osmosis, making room for themselves, much as would be done 

 by bacteria, and when the ligature is gone we have a cord of 

 new living tissue in its stead. Even ivory driven into the 

 flesh is eaten into, digested, and portions removed, by the in- 

 vasion of leucocytes. 



It will be noticed here, as everywhere, when this kind of 

 digestion occurs, the tissue is applied directly to the substance 

 to be digested, and invades its substance as digestion makes 

 room for its growth, so that the tissue is continuously in in- 

 timate relation with it, progressively invades it. We do not 

 suppose that this soluble ferment is pepsin, but a body pecu- 

 liar to the connective tissues, formed only in connection with a 

 foreign substance. 



We will suggest that the sponge graft offers the most fea- 

 sible means of isolating this peculiar ferment. If several 

 sponge grafts were placed in suitable animals, as dogs, and 

 the animals killed at a proper time, and the grafts immediately 

 treated in some way similar to that employed for obtaining 

 pepsin from the gastric mucous membrane of the pig, this fer- 

 ment w T ould doubtless be found. The process would perhaps 

 require to be varied somewhat to suit the different character 

 of the soluble ferment. If this soluble ferment could be had 

 in sufficient amount and purity, it would be of some value in 

 testing the different substances suggested for ligatures, etc., 

 and possibly in ways not now thought of. But the principal 

 use of the proceeding would be the demonstration of a physio- 

 logical process, and the extension of exact knowledge. Such 

 a demonstration would furnish a new basis of fact from which 

 thought might radiate to the unfolding of still other facts, no 

 less important. 



