MICRO-CHEMICAL EXAMINATION OF EXTRACT OP FLESH. 
197 
As there are few chemical operations requiring greater nicety of manipu¬ 
lation than those in which the unstable compounds constituting or contained 
in animal tissues are concerned, and as tlie manufacture of the extract must 
necessarily be subject to variation from this cause, it becomes a matter of 
importance that we should possess some means of estimating, with a certain 
amount of accuracy, the relative value of different samples. Commercial 
reasons also tend to increase, rather than diminish, this variation, for the 
larger product which is often sought to be obtained can only result from a 
proportionate deterioration of the extract. 
Having in previous years presented to the Conference some notes on a 
method which we are in the habit of employing in the estimation of the 
value of vegetable extractives, we propose on the present occasion to offer 
the results of experiments which we have been engaged upon from time to 
time during the last fifteen months, on the micro-chemical characters of 
these flesh-extracts. 
We may repeat in general terms, that the microscope may be made use of 
with advantage in the examination of almost any extract, or solution contain¬ 
ing extractive matter, in which the active or valuable portion assumes a crys¬ 
talline form on inspissation. The fewer the active constituents and the more 
characteristic their crystalline forms, the more readily are they recognized 
and their relative proportions determined. Hot only does the non-crystalliz- 
able extractive matter itself afford no drawback to the applicability of the 
process, but in many cases it really facilitates the separation of the crystalline 
constituents on evaporation. The number of active bodies which exist in large 
proportion in any vegetable or, we may add, in any animal extract, so soluble 
as to remain in an uncrystallized state on the evaporation of a large quantity 
of solution to a nearly solid condition, is exceedingly limited, and even these 
may be detected, as avc shall presently show, by an after process. The one 
essential in the practical application of this method of determining the rela¬ 
tive values of a series of specimens is, that we shall understand clearly what 
appearances the preparation ought to exhibit, and be able to identify the dif¬ 
ferent constituents in the mixed condition in which they present themselves 
to our notice. Hor is it sufficient that we should know the forms and crys¬ 
talline characters of the jpure salts and principles alone ; we must ascertain 
in addition how far the presence of extractive or viscid matters may influence 
their mode of separation. It is obvious that, at the outset, a certain degree 
of familiarity must be acquired with the appearance of specimens, the re¬ 
lative value of which has been determined by other processes, and only 
such previously-tested specimens should be used as standards of comparison. 
It is impossible to argue with any degree of certainty what appearance any 
compound extractive should have under the microscope, and we have never 
succeeded in obtaining precisely the characters we have looked for, when en¬ 
deavouring to prepare, for comparison, any of the complex bodies we have 
worked upon, by the artificial admixture of the constituents. The plan we 
have adopted in the investigations about to be detailed has been almost iden¬ 
tical with that pursued with reference to preparations of opium : that is to 
say, portions of the various extracts have been either mounted for the 
microscope in the condition in which they are found in commerce, or reduced 
to a syrupy consistence with hot water, placed on the glass w'hile still warm, 
and allowed to stand until crystals were fully formed. Tn some instances 
other menstrua than water were used for the better determination of the crys¬ 
talline bodies, and Professor Graham’s process of Dialysis was employed to 
determine the relative proportion of crystalline and colloid constituents. 
The samples of extract of flesh on which observations have been made are 
as follows:— 
