394 E. J. ALLEN. 
sent, and kept under precisely the same conditions, very much less 
growth took place. Here again it looks as if some substance excreted by 
the animals helped to produce a luxuriant growth of the plants. The 
analogy seems complete with what we are all familiar with on land, the 
beneficial effect of animal manure upon plant life. A particular interest, 
however, attaches to Crawshay’s work, because he did not get the in- 
creased diatom growth with other species of Copepods which he tried, 
but only with Calanus finmarchicus. — 
The outstanding feature then of the experiments which I have been 
describing to you on the growth of marine plankton diatoms, is the 
essential importance for the vigorous growth of these plants of some 
specific substance which is present in exceedingly minute quantities in 
natural sea-water and without which energetic growth does not take 
place. This substance, which acts as a growth stimulant, is, we have 
reason to suspect, a somewhat stable organic compound produced by 
other living organisms. : 
And now perhaps you will pardon me if I appear to wander into 
subjects which may seem far removed from my immediate purpose, but 
IT hope I may succeed in showing how intimately the most diverse 
branches of scientific enquiry are often interwoven one with the 
other, and what unexpected light may be thrown upon a problem by 
investigations which at first sight look very remote. 
Much striking work has been done recently on the subject of animal 
nutrition. At Cambridge Dr. Hopkins has shown that young rats do 
not grow when fed on an artificial diet composed of pure protein, starch, 
cane sugar, lard and morganie salts, although such a diet, which we might 
almost call an artificial milk, contains all the generally recognised con- 
stituents of a perfect food. H, however, quite a small quantity of natural 
milk is added to this artificial food the young rats thrive. A minute trace 
.of some substance present in the natural milk makes all the difference 
between growth and no growth. 
Amongst the natives in some parts of Eastern Asia a very troublesome 
disease known as beri-beri has been prevalent in recent years, and has 
caused considerable mortality. It has been shown that the disease is 
directly caused by a too exclusive diet of polished rice. In the process 
of polishing, the outer husk or skin of the rice is entirely removed, and 
with the removal of the husk some substance is taken away which is 
essential if the rice is to be a sufficient food. The disease is at once cured 
by putting the patients on a suitable mixed diet. 
The disease is also produced in pigeons if they are fed entirely on 
polished rice, and some interesting results on the cure of birds suffer- 
ing from it have been obtained by Drs. Cooper and Casmir Funk. These 
