74. DROSERA ROTUNDIFOLIA. (Cuar. VI. 
digested with carbonate of silver. “The weight of the silver salt thus 
produced was only -37 gr., much too small a quantity for the accurate 
determination, of the molecular weight of the acid. ‘he number | 
obtained, however, corresponded nearly with that of propionic acid ; 
and I believe that this, or a mixture of acetic and butyric acids, were 
present in the liquid. The acid doubtless belongs to the acetic or 
fatty series.” 
. Prof. Frankland, as' well as his assistant, observed (and this is an 
important fact) that the fluid, “when acidified with sulphuric acid, 
emitted a powerful odour like that of pepsin.” The leaves from which 
the secretion had been washed were also sent to Prof. Frankland; they 
were macerated for some hours, then acidified with sulphuric acid and 
distilled, but no acid passed over. Therefore the acid which fresh 
leaves contain, as shown by their discolouring litmus paper when 
crushed, must be of a different nature from that present in the secretion. 
Nor was any odour of pepsin emitted by them. 
Although it has long been known that pepsin with acetic acid has 
the power of digesting albuminous compounds, it appeared advisable: 
to ascertain whether acetic acid could be replaced, without the loss of 
digestive power, by the allied acids which are believed to occur in the. 
secretion of Drosera, namely, propionic, butyric, or valerianic. Dr. 
Burdon’ Sanderson was so kind as to make for me the following ex-, 
periments, the results of which are valuable, independently of the 
present inquiry. Prof. Frankland supplied the acids. 
“‘1. The.purpose of the following experiments was to determine the 
digestive activity of liquids containing ‘pepsin, when acidulated with 
certain volatile acids belonging to the acetic series, in comparison with 
liquids acidulated with hydrochloric acid, in proportion similar to that: 
in which it exists in gastric juice. ' i : 
_ “2. It has been determined empirically that the best resulls. are, 
obtained in artificial digestion. when: a liquid. containing two -per’ 
thousand of hydrochloric’ acid gas by weight is used. , This. corre- 
sponds to, about 625 cubic centimetres per litre of ordinary strong: 
hydrochloric acid. The quantitieg of: propionic, butyric, and valerianic: 
acids respectively which are required to neutralise as much, base as 6‘ 25° 
cubic centimetres of HCl, are in grammes 4+ 04 of. propionic acid,:4°82; 
of butyric acid, and 5:68 of. valerianic acid. It was therefore judged? 
expedient, in comparing the digestive powers of these acids with that: 
of hydrochloric acid, to use them in these proportions. 
“3, Five hundred cub. cent. of a liquid containing about 8 cub. 
cent. of a’ plyceriive extract ofthe mucous thembrane of ‘the stomach ‘of, 
a dog killed during digestion having been prepared, 10 cub. cent. ‘of it’ 
were evaporated and dried’ at 110°. This quantity yielded 0°0031 of' 
residue. Be Miss ihe A 22 ‘ Pe ae mtg abe a 
| “4, Of this liquid four quantities were taken which were severally ; 
acidulated with hydrochloric, propionic, butyric, and valerianic, acids, . 
in the proportions above indicated, Each liquid was then placed in a: 
tube, which was allowed to float in a water bath, containing a ther-. 
