1 877.] 
at Home and Abroad . 
101 
that our knowledge of the peptones is no greater. It seems 
to be the objeCt of certain men to test the aCtion of pepsin 
upon all sorts of albuminous bodies in acid solutions, in 
order that when they have obtained their products they may 
pass them through a certain number of tests. These tests 
may be said to consist of the precipitability by neutralisa- 
tion, boiling, or by stronger acids, and by such reagents as 
potassic ferrocyanide and cupric sulphate. But while they 
recognise that these peptone solutions give precipitates with 
bodies like tannic acid, argentic nitrate, mercuric chloride, 
platinic chloride, and plumbic acetate, it seems never to 
occur to them that it would be more profitable to follow up 
any one of these operations, and by so doing obtain, at once 
and for ever, a definite principle by definite means. As it is, 
however, our literature and our text-books abound with 
descriptive matter concerning what may appropriately be 
termed “ test-tube chemistry.” The test-tube as an agent 
in pioneering experiments, as a preliminary to the applica- 
tion of elaborated methods of research, based, indeed, in the 
first instance, upon such reactions, is invaluable ; but em- 
ployed as a final test of character and constitution, these 
reactions are absolutely without meaning. A precipitate or 
a colour may result from the mixture of two solutions, but 
no amount of repetition of such reactions can teach us more 
than the experience of the faCt. To the precipitate we must 
apply methods of purification, and analysis, in order to as- 
certain its composition, and for the colour we must use the 
spectroscope, or other means at our command which shall 
in like manner identify for us its nature. But when we have 
effected all this we have but begun, for it yet remains to 
learn the inner constitution of the body whose empirical 
formula we have established ; even then we have yet to de- 
termine in what way it was in the first place produced from 
the mixture. Then, and not till then, are the resources of 
the chemist exhausted and the problem solved. Now, by 
some of the reactions above indicated, it will appear reason- 
able that phospho-molybdic acid would precipitate many 
peptone solutions, in which case it is not unlikely that by 
the subjection of the products to decomposition with baryta 
water, and further treatment of the free substances, some 
very definite results would be obtained. Meanwhile a gene- 
ral name represents all we know of substances which will 
one day prove to have a constitution, complicated certainly, 
but as evident and as well defined as those of the best-known 
bodies. 
We now pass on to consider another text-book of physio- 
