DIGESTION A SPECIAL FUNCTION. 227 



nature of a solvent fluid secreted by their stomachs ? 

 " It is obvious," says Dr Carpenter, the latest writer 

 on this subject, "that a powerfully solvent fluid is 

 secreted from the walls of the gastric cavity ; for the 

 soft parts of the food which is drawn into it are 

 gradually dissolved, and this without the assistance 

 of any mechanical trituration/' Obvious, indeed, the 

 fact seems, until it is interrogated a little more closely, 

 and then we find, 1st, that no solvent fluid is secreted ; 

 2d, that the food is not dissolved, but only the juices 

 .pressed out. 



My first experiment was to test the presence or 

 absence of a secretion, which was accomplished thus : 

 Tying a narrow strip of litmus-paper round a small 

 piece of recently caught fish, and fastening it to a 

 thread, I gave it to an Anthea cereus, who greedily 

 swallowed it ; another thin slice of the same fish was 

 folded longitudinally over a similar bit of litmus-paper, 

 and given to a Crassicornis. If any acid secretion 

 were present, the paper would redden ; if not, the 

 blue colour would remain. On the following morning 

 the ejected morsels were examined, but not a trace of 

 acid reaction was visible. Eepeating the experiment 

 several times under varying conditions, I came to the 

 conclusion that no acid fluid is present in the digestive 

 process of the Actinise. There still remained a doubt. 

 Solvent secretions are either acid or alkaUne. It was 

 necessary to make similar experiments with an alkaline 

 re-agent. This was done, and with similar results. 



