203 
BPaTISH PHAEMACEUTICAL CONFEEENCE. 
The colloids consist of “ extractive ” and ‘‘ gelatinous ” matter ; and as the 
latter is the more variable constituent, the one chiefly afiecting the quality of 
the extract, it is important that some easy plan of determining the amount pre¬ 
sent should be found. Precipitation by tannic acid would seem to be the 
readiest method, and if this could be done voluraetrieally by means of a stan¬ 
dard solution the quantity might be easily ascertained. Two or three diflicul- 
ties present themselves ; firstly, that of obtaining a perfectly clear solution of 
tlie precipitant; secondly, that of determining the amount of pure gelatine 
which it represents ; thirdly, that of ascertaining the exact point at which 
precipitation ceases. We are only at present prepared to give a few in¬ 
stances of comparative results. Experiments have been made on JN^o. 1, our 
cold-water preparation ; No. 5, the Australian extract, not the same sample as 
previously examined, but a much superior one from the same source; No. 0, 
Messrs. Harvey and Peynolds’s ; and one other sample of English maiiu- 
facture not before alluded to. Taking our cold-water extract as a standard 
represented by 100, No. 5 gave 105; No, 6, 177; and the other sample 301. 
This entirely coincided with our expectation, except in the case of No. 5, 
for the former Australian sample had by dialysis yielded the largest amount 
of colloidal constituents of any specimen we have examined, but even this 
seems to contain a large proportion of iion-gelatinous extractive. Should 
the direct quantitative determination of gelatine by means of tannic acid fail, 
it may still be possible to meet the difficulty by adding the precipitant in con¬ 
siderable quantity; and in a second operation, estimating the excess by the 
process employed by tanners in assaying their tanning materials. 
We are now in position to speak of the actual appearances under the micro¬ 
scope of some of the specimens we have examined. Mere description is of 
little value, and we have therefore made drawings of the more remarkable 
aspects which have come under our notice. 
In Fig. 5 (our own cold-water extract) may be observed the rectangular 
plates and oblique prisms of kreatine, and the silvery prismatic somewhat 
variable forms of what we believe to be phosphate of potash; their fre¬ 
quently irregular ends, showing the laminated structure, remind one strongly 
of specimens, which eveiy one must have seen, of phosphatic salts eaten away, 
as it were, in process of gradual re-solution. 
In Eig. 9 we endeavour to show the results of the re-extraction by alcohol 
of the same sample: a is the portion which remains insoluble after heat¬ 
ing with alcohol; h, the alcoholic extract. In the former, kreatine and the 
phosphate are the most conspicuous objects ; in the latter, a portion of the 
kreatine in smaller crystals may be observed with a considerable quantity of 
chloride of potassium in its characteristic forms. 
Fig. 6 represents our own hot-water extract, which appears under the 
microscope as a dense magma of crystals, so dense as almost to defy drawing. 
Its opacity in comparison with cold-water extract is clue in part to its slightly 
higher colour, and is partly owing to the increased thickness of som.e of the 
crystal masses preventing the arrangement of a sufficiently thin film. It is 
similar in its constituents to the cold-water extract, but the crystals are more 
irregular in shape, and therefore less easily recognized. 
Eig. 7 represents Messrs. Harvey and Reynolds’s extract, and ofiers few 
points demanding remark. Its crystalloids are of a somewhat less decided 
nature than in our experimental samples, and are not present in quite the 
same abundance. 
Eig. 10. In this we show the Australian extract, and its relations to the 
alcoholic test: a being the portion insoluble in alcohol; 5, the alcoholic ex¬ 
tract. The latter is not arranged, as most of our drawings are, with the idea 
of showing the appearance of any single field under the microscope, but rather 
